When you say function, you mean, "it protects my feet from broken glass and concrete, is easy to put on and take off, and feels good." You've defined 'functionalism' to mean the effects of the item on you rather than including its effects on others. The functional uses of fashion (being attractive, being liked, being approachable, raising the aesthetic average) are very powerful in any location with people around.
Some fashionable alternatives to sandals with socks: boat shoes such as Sperry Top-Siders, loafers, or generic slip-on shoes such as Vans, potentially combined with no-show socks or flesh colored ankle socks.
Note that fit requirements are important for shoes as well - many people don't realize that their feet require more or less width than is found on a normal shoe. If your toes are constrained, you could try different half-sizes and widths.
Rain said:
You've defined 'functionalism' to mean the effects of the item on you rather than including its effects on others.
Excellent point. The notion that the "function" of fashion is merely one's own comfort is incredibly strange. This kind of thinking may be the consequence of all the public fictions about status (e.g. "it's what's on the inside, not the outside, that counts", "clothing is shallow, intellectual pursuits are deep").
Thanks to these public fictions, lots of intelligent, technical people just want to opt ...
Yesterday I attended a meetup where the discussion turned to fashion for a time (because apparently the mini-camp participants were given some instructions on fashion as a useful part of instrumental rationality). (Unfortunately none of us knew much about the topic so the discussion turned into "how can we find an expert to advise us for minimal cost?") It was mentioned that dressing "badly" can be a useful signalling device, and some examples were given. Here's an attempt at a more complete list of possible signals one might be sending by dressing "badly".
The idea here is, if you do decide to start dressing "well", know what you're giving up first. (Of course you're also giving up possibly implying that nobody taught you how to dress and you're not sufficiently strategic to have thought of learning it yourself. Or implying that you don't have the mental, financial, and/or social resources to keep up with fashion. A lot of signaling depends on what your audience already knows about you, or can infer from your other signals.) See also Yvain's related post, Why Real Men Wear Pink and comments there.