concerning how so many claim that the institution of marriage is somehow degraded by opening it up same-sex partners. There isn't any logic to it, and whenever I ask a hetero married person who has just expressed the view how exactly it degrades his/her marriage, there is no response other than an occasional 'it just does.'
On your other points - no argument here. I was a 'family law' attorney for two years, which was about a year longer than I could really endure it. Frankly, I do believe that marriage ought to be for life, in general (not perhaps the best perspective for a divorce lawyer - probably had something to do with my need to get out of the field before I went bonkers).
In the end, though - marriage is definitely an important institution in our society and always will be. Even though this is true, it's based generally on the extremely frequent occurrence of two relatively young people becoming very attracted to each other, which leads to a strong and temporary emotional/physiological/neurological change in the parties, as they fall in 'love' and decide that they want to spend their lives together. The temporary state eventually subsides, and hopefully the parties find that all of the potential problems that they couldn't or wouldn't see early are very real and must be approached. Some do very well, some don't. Divorce is there, more and more often in our society, for those who don't try very hard to work things through.