I wouldn't disagree at all., in fact I think some of them are silly right now, especially the pirate metal offshoot of the genre. I enjoy Alestorm, they're a fun band with quality music...but half the kids that show up to their gigs dressed like pirates probably wouldn't even admit to having ever been a fan in 5 years. Same goes for Swashbuckle, minus the "fun band with quality music part".
As far as pagan/folk metal, I don't think it's their outfits/gimmicks alone that will cause the backlash, it's the popularity bubble that's inevitably going to burst. Once people realize the genre is over-saturated, there will be a whole batch of jokes about guys in kilts, war paint, whatever it may be.