This would kill it for me. I've spent my whole adult life learning to use graphite and charcoal, oil paint and clay. Having my entire effort refused because I don't know what a GIT is just doesn't work for me.

Having communication barriers like this absolutely would stop me from participating. I have no problem with being asked to redesign a logo over and again. I would love to feel like I belonged to a community and that I mattered. But having a developer jack my work and screw it up because it was easier than asking me to do it would completely scare me away from open source projects.