If she was going to the beach or a BBQ, then you're right, there is nothing improper with what Witt is wearing. However, she's a big time news anchor on a major news network, and instead of presenting a professional image as a respected journalist, Witt chose to look like she was attending a garden party in that frock.
Yes, she might be "a fairly attractive lady wearing a nice outfit", and again, that's the point, she's not hosting a lollapalooza fashion sale on the Home Shopping Network, yeah? Look at most TV anchor hosts, they are very professional and conservatively attired in unremarkable, dark, muted clothing choices.
This is not a question of us "do-gooders making a issue out of it", it's that some of us still think that its important to respect the value of journalism, a profession that is under constant attack by rightwing sources. Let not defend Alex Witt as she swings her news show towards the Fox News business model, where women really are cast as on air personalities based solely on their looks and their silly gyrations in keeping those too tight red dresses from revealing everything.