It can not be stopped because altcoins allow anybody to make them you don't even need to have any skills or anything special ,the big difficult here is to be able to gather money from investors, you need to show that your product will be successful and they are most likely to make money on their investment.
The real problem with junk altcoins that they usually aim at newcomers, they show them an attracting youtube video to make them invest, and they usually don't have any real idea or real development team to make the project actually go live.

Altcoins are very dangerous and involve a much higher risk level then investing directly in bitcoin.