I think you're right. Personally, when I joined the ICO, I was very interested in the whitepaper of the project. I am really afraid of joining ICOs without a whitepaper, they are not credible
But what about those trying-to-be-legit icos that have a whitepaper yet turned out scams? They try to look legit so they can lure the people to invest in their project. IMO, if an ico really tends to scam people then it will be, no matter how attractive their project neither the team.
I'm not saying without whitepaper is good nor we should be more extra cautious in choosing. Remember that before, bitcoin doesn't have a whitepaper too and it came up when it's already in the market.
Perhaps you can find good ICO without white paper, but you are right, we must be very careful when choosing a project, and pay close attention to analysis.