I have no issue with light armor. Liara's shadowbroker outfit is one of my fav armors in the game. I just really don't want stupid rule of cool armors. Outfits on the ship? Fine whatever. But combat outfits? =/
Edit: The following is not directed at you Fiend. 
Also the whole sex appeal as defense with Miranda is stupid considering the main enemy of ME2 were freaking Collectors. The Collectors wouldn't give a damn if she ran around screaming naked. I refuse to believe Miranda of all people would armor herself up for only part of her enemies.
I'm not claiming Miranda's suit offers anywhere near the protection that Vega's armor does, but, stilettos aside, I still see it as somewhat practical. Given that in real life we're currently developing bullet resistant materials as thin as human skin using spider webs, it doesn't strain my imagination that well over a hundred years down the line, we've got something as thin as that cat suit that offers a modicum of protection.
Now, I'm not claiming it's anywhere near the same protection as Vega's armor, but again, these characters are biotics who specifically rely more on barriers for defense than armor, and I'm willing accept that she, Jack, Thane, and Samara decided the trade off added mobility during a fire fight - getting from cover to cover more quickly, not having to deal with the fatigue of slugging around in the armor, things like that, was worth it. Given how effective armor is for everyone who goes against Shepard's squad(read: it isn't), that's not an unreasonable stance to take.
Also have to remember that none of these characters(Except Jacob, and he's the most borderline case) are soldiers - I mean in terms of profession, not class. Miranda's a project leader and scientist who happens to be combat trained. Jack is a criminal. Thane is an assassin. Samara's a bounty hunter. So ignoring that they all have biotics to compensate for their lack of protection, they're also all in lines of work where armor is more often than not a liability, or at least not necessary, so it makes sense that they're less accustomed to wearing it than the soldiers on the team.