It's not "just because I disagree". It's overwhelming reaction to those valuations among tech community. For example here on HN you see a lot of people joking a

It's not "just because I disagree". It's overwhelming reaction to those valuations among tech community. For example here on HN you see a lot of people joking about those valuations and many (most?) consider them completely unreasonable. Either they are wrong (quite possible) or there are naive investors in every case (quite possible as well) or there is some other explanation (out of which fraud is natural one to consider as it would make investment based on ridiculous valuation rational). You may be on opinion that the valuations are clearly not ridiculous and that's fine but imo you can't rationally claim that valuation is ridiculous and fraud is not serious possibility.