I recently loaned one of my 6-string banjos to a lead guitarist who can play rings around me in almost every way. I thought he might figure out what it was good for. And he did. He adapted several of his guitar styles to it, and took it to any number of venues, only to have the folks there including band mates and "friends" say "why didn't you bring a REAL banjo?" He has since returned it.
I didn't know he was getting such grief, or I would have given him the answer for his "friends": "Six-string banjo has been around almost fifty years LONGER than Bluegrass. Don't talk to me about 'authenticity.'"
I just wrote two articles about 4-string guitars, which were made by Gibson, Martin, etc. to the same standards as their six-string guitars and marketed to jazz banjo players who wanted to double on guitar. "Tenor" and "Plectrum" guitars had the same tunings, number of frets, etc., as the tenor and plectrum banjos of their day. Most banjo players who migrated to 4-string guitars played them exactly the way they played their jazz banjos. For a while they far outnumbered the 6-string jazz guitarists. In fact, you could make a case that the tenor banjo rage of 1910-1925 was the direct ancestor of "jazz guitar" as we know it. Yet, when 6-string guitar players see a real 4-string guitar (not the oversized ukuleles that some importers are making), they do NOT say, "Why didn't you bring a REAL guitar?" They tend to say "Cool, can I try it?" If you told them it was "really a banjo," they would look at you as if you were stupid. And rightfully so. It's made like a guitar; it looks like a guitar; it sounds like a guitar; it IS a guitar.
So why do six-string banjo players let people who only know one tiny part of the musical universe bully them into saying, "It's really a guitar" at every opportunity. Sorry, a 4-string guitar is still a guitar, even if it's tuned EADG. And a 6-string banjo is still a banjo, even if it's tuned EBGDAE.
On the other hand, Mark Twain once said you should "never argue with an idiot. People watching might not be able to tell which is which."