Serious question - do you want to see FinTech succeed? Because if you do, then raising concerns like that, when you do know better, is only going to put people off the startups.
I’m not saying that you shouldn’t share your feelings. But you could at least acknowledge the fact that they’re irrational & maybe even mention why - share your knowledge & make a positive contribution to the discussion. For the benefit of other users who aren’t sure whether using these company’s services is safe.
Edits - added text in italics