My imagination allows for technology and biotics to compensate for that, to accept that the rules of nature work slightly different or are more advanced in the Mass Effect universe than they are in our world. My immersion doesn't depend on "realistic" rules of nature, but on the game atmosphere, the characters. I'm all in favor of options though, for those lacking the ability to handle a world slightly different from our own. But, I'm getting sick 'n tired of the "that's not realistic plox change" demands I see from a handfull of whiners about every game these days.
Since resources are limited in game development, there's a fair chance that outfit options aren't available. And given the choice, the ME universe should stick with what is already established there, rather than making it as drab and boring as about every other sci-fi title currently available. So yes, in the ME universe, a breather mask suffices and high heels are as functional as flat boots. If the designers have resources to spare, sure, they can add some of the boring standard options that other games have. If they don't have the resources to spare, then the boring conservative options should be the first to be left out.
Except those outfits don't fit with the established lore of Mass Effect universe. It clearly states that biotics and shields can't protect from hazards of temperature and atmosphere. That's why Shepard wears sealable armor with a closed helmet in such environments and seeing his squadmates disregard that breaks immersion.
Mass Effect universe introduces a clearly fictional Element Zero to the real world and builds upon that. Everything else is quite possible with even today's technology, even medi-gel.
If they change the lore to allow people walk around in space in breather masks (canon Synthesis, perhaps?), I won't like it but I'll accept it. So far, the lore does not allow that to happen and situations, like the one described above, break suspension of disbelief.
And no, I do not argue against "oversexualized", "slutty", "progressive" etc. design of the outfits. I argue against outfits not fitting within the established fictional universe in certain situations. To fix that, they can remove those situations, replace the outfits, change lore. I'll be fine with the first two options, not so much with the last.