It's only fair to let you guys have a go at this.
Why do people compare guns to penises? It isn't a simple question and there isn't a simple answer but I'll give it a shot (yeah, that was a pun). Before I wander off into this flamebait fraught topic let me say clearly that I do not believe that ALL gun owners are compensating for anything. There are no absolutes when discussing entire classes of people. That said there are some pretty good examples of overcompensation that even the most ardent gun rights supporter has seen and recognized.
Start with the biological imperative. Females of most species seek a mate that exhibits the epitome of virility and strength. These traits are essential to the preservation of the species as they represent the strongest gene pool. Physical strength also provides protection from predation while she is encumbered with offspring. So, okay, strong and powerful is good. This is also not an absolute; in one species of cuttlefish the small weak male can disguise itself as an immature female and is ignored by the large dominant male while it invades his territory and is rewarded by the female with the opportunity to mate. Seems that intelligence and cunning can also be attractive traits.
Climbing up the evolutionary ladder to humanity some of the biology remains. In Victorian times and up to the 1950s when women were relegated to a secondary roll in society a powerful and successful husband was the key to a happy and safe home life. This is essentially the premise for vampire literature; a handsome wealthy man that is invincible, lives forever and can bestow the same on a mate is the ideal provider for a Victorian woman. Needless to say none of this is still biologically necessary as women have largely come into their own for success in business, politics and equality thanks to the Feminist Movement. I say largely because there is still that 78 cents on the dollar thing and rape culture but that's another flamebait quagmire.
A gun is a symbol of power. Power is symbol of virility ergo a gun is a symbol of sexuality. There are a lot of other symbols as well, the sports car or taking up dangerous hobbies so emblematic of mid life crisis but we're talking about guns here. I'm sure these guys would rather have a Corvette but an AR15 is only about $700 compared to $40k for the car.
The literature of psychology is full of power symbols relating to sexuality. Freud and Jung explored the relationship of weapons to sexuality as evidenced in dreams. Pick up any introduction to Psychology text. But remember what Groucho Marks said, "Sometimes a cigar is just a cigar."
How are guns marketed to men?
As symbols of power:
As symbols of strength and protection.
As things that scantily clad attractive women enjoy fondling.
As things that women use to attract men, presumably powerful men.
And of course this most patent of all pandering to the possibly penis challenged.
?w=466
Now, if any of this offends a gungeon dweller let me repeat; I do not believe that all gun owners have penis deficiencies. I mean what the heck, I own a bunch of guns but I'm not this guy:
But I do owe Kory a note of thanks for singlehandedly defeating Constitutional Carry in Texas.
= new reply since forum marked as read
Here on DU?
Because they can do so without fear of consequence, due to it being an accepted form of sexism and bigotry.
In kind of in the same way...and by the same people...that openly support bloombergs astroturf groups, in spite of his racist remarks about minorities and his groups inclusion of one of the terrorist boston bombers as a "victim of gun violence".
Its been going on for years, decades even, but it is in large part, responsible for the numerous victories the anti-gun crowd has won. 
I say "Onward, anti-gun soldier". 
immaturity.
It titillates a receptive audience to conflate guns and sex as a compensating thing- if a person views guns negatively, or as a proof of manhood- if the view is positive. In both cases the relationship between gun ownership and any sexual trait is approximately equal to zero.
As for why are scantily clad women used in firearms ads- simple, sex sells. It is an old and well known/used maxim.
A body wash is only going to lead to orgasm if the cleaning is focused
Will you become a supermodel/have a relationship with one if you are a vegetarian
Or perhaps meat will... nevermind, it's pretty self explanatory
Although there is a trend beginning to equalize exploitation
Some are blatantly honest
But it is not new
If only they knew how much farther it would go
And yes, if anybody should get on a gun control payroll it is Kory...
well at least in that post that is just so smoking hot over in "bansalot" And of course we are all right wing trolls, no insult there, right?
Bjorn Against
That group is filled with right-wing trolls, don't let them get to you
There is one in particular that I have noticed loves to harrass the hosts of this group every chance he gets, he loves to lecture about politeness while being completely oblivious to the fact that his constant harassment is anything but polite. I have seen him jump on you multiple times over an alert he had against himself, and he constantly harrassed Secular Motion demanding he "discuss" with people who clearly just wanted to tear him down.
Why the admins allow people like this to harrass good standing members of this site like he does I will never understand, there are several people in that group who should have gotten the boot long ago.
Asking a person to answer a question is harassment now?
Simple fix, answer the fricking question
So is asking a host to follow the group SOP?
Simple fix, Follow the frickin SOP
Who knew, the humanity.
Funny how neither him or his colleagues ever chimed in about loudly/sharesunited.
One of the most, if not the single most, obvious retread to ever be seen on DU.
Evidence was provided and presented numerous times in numerous forums, and yet all we heard from the usual suspects is:
How about anyone that just can't seem to restrain themselves from a generally untrue, somewhat offensive, outside the actual SoP of the group reference(s) just to fit in their own quip, which doesn't have nearly the same attention getting effect for those class clowns among us, how about those folks just start their OP title with *PENIS*?
This seems like a great way for ATTRACTING-ATTENTION-TO-YOURSELF. 
(r)George Carlin
Said class clowns can then add their two cents with or without the typical cartoon, reference, joke, link, etc. This may save some folks quite a bit of time searching for 'google: nasty gun penis cartoon' and such.
is a "game."
I thought my last post was a good question to bring the discussion back on track: the OP states that "people compare guns to penises" and it would be worthwhile to know specifically which people and which comparisons he was referring to. All the overt gun=penis references I have seen are from anti-gun types attempting a base and sexist insult, and have nothing to do with the behavior of gun owners or the marketing of guns.
There's a lot of tangential discussion here about sex in advertising, but it's a huge leap and a red herring to conflate that advertising with the gun/penis snark - two topics entirely, and the advertising does not explain, cause, represent, or justify the sexist 'teeny-peeny' snark...
(If the OP intended to limit the focus only to sex-centric advertising, that intent certainly wasn't clear. And I don't think sexualized advertising of guns is any more equivalent to 'comparing guns to penises' than sexualized Burger King advertising is making a burger=penis linkage.)
