How can you "refuse to allow" anything? Anybody is allowed to fork an open source software. If the community is not interested in the fork, they don't need to use it - simple as that. Unfortunately, the exchanges don't want to miss out on trading commissions, so they'll list anything that will make them money.
The fact is: It's a free market. Exchanges are free to list whatever coins they want. Investors can buy/sell whatever coins they want. Eventually, people will grow tired of these shenanigans and will start to understand that these forks are just cash grabs. And then money will flow back into cryptocurrencies with strong fundamentals, like Bitcoin. Newbie investors who wanted to get in on "the next Bitcoin" are going to get fleeced and lose a lot of money.