More exchanges = more options = more chances to get scam = more wisdom = more demand for decentralized exchanges = more decentralized exchanges
Wrong, less chance you mean because with more exchanges, you have a lot of option on what exchange you will use, of course you'll use the most trusted one.
Maybe what he mean is with more exchange there are bad and good exchange, it means there are a lot of chance we will use that scam exchange, like when our tokens only listed in there and then the site closed with some reason. Maybe what he want to say is like that, because we should see positive and negative impact from something like this. So we not get scammed.