You really think it is okay to say “I will try project A, I need donations” and then go on a holiday with the donated money and do nothing else?

Yes. A donation is a donation, fullstop.

Would I feel good or morally okay doing such a thing? Absolutely no way. I acknowledge that internal inconsistency. If someone gives me something, I feel obligation to give back.. simple as that.

Objectively speaking though, a donation is not a contract, and to expect a donation to have future influence is a messy method of doing business that should be viewed with a pretty critical eye. If a person giving money wants an obligation, they should pursue a contract.. If they don't care what happens after they give the money but just want to show support or appreciation, that's where donations shine.

If I gave a donation to my favorite videogame dev, but then 2 hours later they stopped supporting that game, I'd still be happy I showed them support for what they had given me so far. I believe retroactively being unhappy about giving a donation shouldn't cast the receiver in a bad light, and that it's the giver that didn't understand what they were doing and what the potential outcomes were.