Unfortunately, some people don't have the luxury of departing or hopping into a dream job with tech savvy, understanding middle/upper management. There are certain social hoops to jump through from time to time, especially if you want to pay the bills or meet a personal objective. [Ex: I'm going to work at this upper tier but stuffy design firm so I can build the resume required to work for the XYZ firm I'd prefer to]

No one is questioning how you spend your personal time, I think the debate is the idea of advertising it on a veritable public forum. Maybe your twitter account celebrates your depraved (but legal) sexual fetishes, or even something more innocuous as a political agenda. If that is something you don't mind sharing with employers, great. But I think the point is that there may be repercussions for your actions. Some people may take greater stock in a snapshot of your character, others might take a more realistic approach.

I'd rather err on the side of caution, and keep my work and personal life separate.