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.
I am of the opinion that, had it been that Bitcoin was the only cryptocurrency, it would have been harder to gain even up to the number of investors it has now, because the risk of it crashing would have been way higher, the blockchain would have been used for other projects that may be too advanced for many humans and the cases it would have battled from government would have probably discouraged even the brains behind the BTC idea to pack up shop and disappear.
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 that after such sad experiences would go back, research and get onboard.
The competitive environment that the Blockchain network has enabled for crypto currencies to thrive on, has more than made people have a better perspective on why Bitcoin is, and remains the best crypto currency among others, upon a conclusive research.