Some tokens are tokens of excellent ICO projects that have great prospects for growth and their capitalization at the moment is greater than that of many altcoins.
How can they not be trusted?
I don't know but for me, not all erc20 can be trusted. I mean it's now easy to create in this blockchain and some are just using their token to launch an ico and scam people. Just trust those who are established and think many times in those new tokens that popping up in the market. I can see NEO and EOS will be a good competitor of erc20 so no doubt it will be a huge success, eventually.
ERC20 token itself can be trusted but those who use it for scam are not trusted, but not all are scammers there are also more tokens that succeed now and still running until now.
Yeah, I think we should not generalize the erc20 tokens. There are others which are legit and successful ones. It is our duty to do our own research aside from watching and reading reviews from legit sites and personalities and select the right one to invest.