Why bother creating new music? That's different, though, from saying people should give up on exploring the options, just because they probably won't make any progress that hasn't already been made by someone else before; or worse still, that there's something wrong with a person who would dare even try that. — Pfhorrest
If this is all you're frustrated with, then, of course, stuff the naysayers. Feel it roll off your back as you continue forward.
It's actually less common to find in the music/art world; innovation and newness are names of the game in my world, so I find it odd to encounter something like what
@TheQuestioner is saying. He just sounds disillusioned, which I don't think is the same motivation behind your philosophical naysayers.
As to fossilization of understanding being good...yes and no. Falling into a mystical pit of everything and nothing isn't healthy, but neither is the fossilization of your understanding to the point that you cordon off legitimate paths, causing blind spots that you'll have a hard time undoing. This is what I see the most of in philosophy. To use extremes, it's the analytic who can't even entertain the theoretical possibility of something mystical (either out of fear or hubris), and likewise it's the religious figure who can't engage scientific enquiry because he's afraid it will destroy his worldview.