Yes, it is unreasonable. You could say that any business "might [be] using the cash influx from newer users to cover cash outs for older users." Seriously, don't hide behind the word "might." It's a lazy defense of an accusation that's based more on emotion than reason or facts.

I once ordered a computer from Dell. The sealed box arrived empty. I went through few weeks of increasingly enraged emails and phone calls. Should I have assumed Dell was a Ponzi scheme?