I think I would be more worried about bubba the redneck and his reaction to wearing Lycra!
On the Southern Tier I had absolutely zero issues with that. Not so much as a snide remark.
Also I saw more artsy types and hippie types on the Southern Tier than on the Trans America or anywhere else I toured. Marfa TX is an artists community and in Marathon TX I stayed in a really weird commune.
I have not had any real problems anywhere I have toured, but the Southern Tour I didn't even get any funny looks that I noticed. It wasn't substantially different than anywhere else in the rural US, but if anything it was better as far as any negative interactions with locals. I stopped and chatted with many of the locals all along the way and the interactions were universally positive. Of course YMMV.
If I wasn't worried about doing all that 'hard work' to get it where it is now, I'd shave it again just for the convenience. But its been a few years and don't want that in between length. Btw my first thoughts about having long hair and riding was that get tangled up. Even tied back. So I have adopted some kind of tiered ponytail system and works pretty well, though if I knew how, would also try a single monster braid.
Glad to hear you got along just fine down here. Makes me feel good, but doesn't hurt to be cautious sometimes. There are all kinds of folks and in all kinds of places.
I have no problems with my long hair while touring. Granted washing it is not always easy (drying takes a while sometimes and if the weather isn't warm it is no fun) but it quite doable.
As far as idiots who dislike long hair you could run into that person anywhere at any time but generally not going to happen. I figure anyone who might be that type of person would more be fascinated that you have one of those "wheely pedley things" and you "done rode it that far and you go'in where?". For the most part people have semi-evolved, in a small way, enough to where long hair on a guy is not something to mention at the very least.
If you are the type to be willing to get your hair cut, you might want to get it off and let it grow back along the tour to make it easier and cooler on your head. However if you are like me and won't cut your hair for any reason (though I do trim my muttonchops/sideburns and shave in the non sideburned areas) then I don't think you will have any major problems. Bring extra hair ties and use Dr. Bronners (multi use soap that cleans hair really well amongst many other things) and have a small tube of conditioner and you will be just fine.