I guess you're right, it's a flawed argument. In fact, considering that I use exactly your argument to support/demand not eating meat, I guess it shows that I

I guess you're right, it's a flawed argument. In fact, considering that I use exactly your argument to support/demand not eating meat, I guess it shows that I might just be going for a post hoc rationalization of actions that emotionally appeal to me in this case. But just to play devil's advocate, might the charity decide that they want to take in a certain amount of money from an event and set ticket prices accordingly, thus passing the cost on to attendees? (The implication being that it's less ethically dubious to leech off of rich people than charities.)