No, I don't think so, I would rather say that altcoins have helped the adoption level of Bitcoin greatly because if there were no altcoins at all, it would take more time for Bitcoin to spread around and it is altcoins that make Bitcoin look better because people compare altcoins with each other and also with Bitcoin, and when they find out which one is the best, which is Bitcoin, of course, they become more interested in Bitcoin after that.
Actually, I don't see it that way. I'm quite aware that there are good altcoins but if Bitcoin was the only cryptocurrency there won't be any scam and perhaps the adoption would have increase. Some persons who got introduced into the space invested in the wrong projects and after getting punched in the face, I believe such persons would convince anyone that comes his or her way not to invest in Bitcoin because he would think bitcoin is also a scam. It's just few of them after such sad experiences would go back, research and get onboard.