When it comes to military uniforms and paraphernalia, that's a very thorny ethical issue I can't do justice. However, I do have some thoughts related to:

Do any of you wear replica clothing for its function? What are your experiences with people wearing replicas that may not have actually been apart of that era?

There's a certain perception out there that crops up in comment sections and response pieces whenever an article is written about "vintage lifestylers", people who dress only in vintage clothing or home-made reproductions ("repro" clothing purchased from retro vendors being generally inaccurate and often having the same issues as ordinary modern clothing), cook historical recipes, use midcentury-modern furniture, etc. The most extreme version of this would of course be the Chrismans, of That Vox Article about people living the Victorian life in the Pacific Northwest, and the reaction was similarly extreme, but you can see in it a stronger form of the response to weaker forms of 1940s-1950s vintage lifestyling. That is, that a preference for historical aesthetics or function - while your example of neck flaps is a more obvious use of "function", I would consider clothing that fits better or allows a certain type of movement to be a matter of function as well - necessarily indicates a personal ideology that fits in with the socio-political norm of the period. The assumption by many in the mainstream is that a 1950s exterior is indicative of a 1950s interior, complete with regressive gender roles and misogynist standards, although it's by no means true of all or possibly even the majority, given the number of people involved in "rockabilly", vintage's sexier, punk-ish sister. But it does read as offensive to some people who believes that it's whitewashing or glorifying the past (though it seems less offensive than when coupled with apologia).

Now, I have to admit: I wear historical clothing on a daily-ish basis, ranging from dresses I've made myself from historical patterns to good repro (I'm wearing this right now) to modern stuff with a vintage look, I have a middy haircut that I wet-set in pincurls every night, and my favorite cosmetics are made by Besame, so I have a strong personal bias here. I wear replica clothing for its function in the sense that I laid the definition out above - it tends to fit me better and be cooler in the summertime, and the full skirts allow more leg motion than jeans or dress pants. Nobody has ever expressed their offense to me about it.

This is all somewhat orthogonal to your example, but as your overall question was vaguely worded enough to include all historical/replica clothing rather than only military uniforms I hope that this is useful to you in some way.