Is a mustache unprofessional even if within regs??

Takes a mustache, even a bit droopier than 670-1 permits, to be an Aviator Warrant...take a look at the Army Viet Nam era pilot?

I think when we get into these sort of topics, we're un-casing the "unofficial" rule books. In the Navy, there are times when regulation mustaches are not only considered "professional"... but even "traditional". Aviators routinely grow one when they go out to get their trap quals, and it "used to be" traditional to grow facial hair on a submarine during deployment (though I suspect that's changed). That said, my own experience was that you RARELY saw one on any officer who was not a "mustang", and even then-rarely among JOs. Some may disagree with me, but personally... I always felt that if you saw an O-4 rocking the 'stache anywhere in the Surface Line...he was probably a former Chief, and probably in Deck or Engineering department. It seemed people who were being "groomed" for flag officer stayed very clean shaven; the one exception being a prior enlisted O-6 and Academy grad I knew who wore his grey hair and mustache with pride... right into getting his star.

I'm going to respond to this with similar same words I commented on another thread about professionalism:
I will say that a LOT of things have been labeled "unprofessional" in the last 10-15 years. It seems like half the Army mid level leaders are clutching their pearls. It is almost an unhealthy obsession. Some of these things have even found their way into regulation.

I won't say do not listen to your leadership. The term "Choose Your Battles" gets used often, along with "drink the Koolaid" (I despise this last expression because I remember it's source).
I think the point is that just because someone dislikes something, especially our leadership, it doesn't mean we've actually done anything wrong. While you're serving under them you will have to play by their rules, however it should not imply that you've done anything wrong.
I would consider what actually brings discredit to the uniform.

They are not, insecure weaklings just can't handle them because they feel intimidated by traditional assertions of manliness.

I think there are bigger fish to fry than worry about my stache.

Plainly stated....no.

Yeah, another one of those overworked nonsense words..."professional"... I call them inventions for the unenlightened and ill informed! Long hair went away because it was too easy to grab in hand-to-hand, most facial hair went away because a gas mask won't seal over a beard and a long moustache shoots up the nose inside a mask... there are valid reasons for things and then there are the total nonsense blather that has developed to replace reason... I really wish people could tell the difference!

Personally I stayed away from having one b/c the regulation for one was too strict...you couldn't grow it the way you wanted to....couldn't be beyond the edges of your mouth...can't be bushy looking etc...so I just stayed away from it altogether...I think the arguement most people bring up is other Armies do it... so why can't we etc etc etc...then we get into the whole NBC Mask thing...that Sheik can have a full faced beard why not I??? etc etc etc...Garrison vs Field environments etc etc etc...I just didn't want to deal with the baloney...Keep it short and shaved everyday...

Unprofessional, No. Gross, Yes.

Personally I have zero problem with any man growing a mustache regardless of rank as long as it is within prescribed standards. Professionally, I know some bits of gear are not as functional when wearing a mustache such as a diver's mask. But if the swimmer can still preform their mission, I see no issue with it.
I am not being mean spirited with this next comment nor am I trying to be funny. Equal opportunity for women is such a contentious subject these days and growing facial hair may become another one. Currently, I do not believe there is a standard for women and mustaches. I expect that it must be the same as for men. And yes, I know of several women who wear them now.