Vegan, vegetarian, hand jobs... Each misses the point. The point is that it is exploitative to say "I have tons of money. Take on my cause, and I'll make your problems disappear." Opportunism, war profiteering, etc., are always offensive, because they can be seen as taking advantage of the less fortunate to advance yourself. In this case the fact that they ostensibly want to advance the cause of animal suffering muddies the waters, because some people think their cause is a just one. Some people think that converting people to Christianity is a just cause. Would it have been appropriate for the Vatican to step up and say, "We'll make your water bill disappear every month that you come to church at least 6 times"? Could Sheldon Adelson say he'll pay the water bill of anyone who votes republican?

We come from a nation of charitable people, and I think we should be proud of that. Most people who can afford to give some amount of charity do so, and those that do rarely ask for anything in return. It's part of our being to help the needy, so to dangle the carrot that's only available for a quid pro quo is inherently offensive, not offensive on the merit of the cause.