You can lose 100% if you're completely scammed and the price drops literally to 0, which isn't the case for any ICOs I've seen, even scam ones.

Earning potential is strictly limited by many factors, it's false to say otherwise. It's true that some ICOs will have large returns, but few actually outperform the growth of Ethereum. When comparing ICO value to the value of crypto as a whole, most are not very good investments (and that's while ICOs are in their prime right now, when the ICO bubble bursts it's going to be much, much worse).