Maybe bitcoin will be more successful without the altcoins because people will be focus in just one cryptocurrency and demand will focus just in bitcoin that will can to spreading bitcoin in a fast development and i guess will get a very high price so fast.
You might think like that but it's better that we have altcoins. Altcoins spam twitter and FB like crazy. Altcoins aren't just advertising their coin but they are advertising the cryptocurrency as a whole. That makes people know about bitcoin. If there's just bitcoin, people aren't going to spend a lot of money advertising bitcoin just so the price of bitcoin will pump[1]. We all know that ICOs make a lot of money for the developers. I'm starting to think that some people out there are just making new and new coins to make more money.
[1] And ultimately helping the price of bitcoin go up by advertising it a lot will just be a waste of time because you are not the one who's going to make profit out of it. Other people will. Other people will always sell before you.