They are good for the crypto market ecosystem, but if the number of coins that do not meet expectations is too wild will have an impact on investor confidence in the next new coin related to ICO that is being run.
They are bad for the market. I can cite a hundred reasons why having a million shitcoins for the same system makes them redundant and a source of investor scams. Everytime a new coin comes out with some new age Bullshit agenda, some koolaid infuser comes in with their conspiracy theory of why that coin is going to take over bitcoin. Sometimes give me a good laugh.
For bitcoin and other altcoins, it will not have a significant effect, because the holder has strong trust in the coin (loyal holder).
Bitcoin does not even come into this picture. All of the other coins are just plain koolaid teams. If you want to hold something that is not shit then just buy and trade bitcoin. As simple as that.