I hadn't thought about that. You would actually need receipts showing you donated the money to a charity. Or form your own charity.
It is impossible to be completely legal in the US today regardless as most people commit multiple felonies a day without even being aware. As soon as you are aware of this than the only thing you can do is protect yourself and mitigate those risks reasonably. Some people will choose to avoid Bitcoin altogether for this reason but if you compromise your values than that is removing the need to protect anything at all because you have already given up what is most important.
Starting your own non-profit can act as a complicated hassle and not necessarily prevent an indictment if the numbers don't add up. The safest bet is to just mitigate the risks and not deal with sell to people who claim illegal use , and keep transactions under 10k for strangers.
If you think this kind of shady dealings makes bitcoins more popular towards mainstream ordinary people, think again.
We don't need another fiat, w/u, or paypal.... we already have plenty of those options. If Bitcoins core principles scare the mainstream away than so be it, I would rather have slow and steady adoption and keep the principles which make bitcoin valuable and useful to me than treating it like some get rich early investor stock.