Donors come to expect receiving some manner of restitution for the service they render. Because someone is wealthy and can afford to donate money for a team or business corporation, does not give them the right to play or work above someone else who is more deserving. In many views, this is morally wrong for our society to sulk to.
Coaches of sport teams can be greedy and corrupt, players who work the most throughout the year and players who do the most physically and mentally for their team deserve more playing time than a player whose father donated fifty-thousand dollars to the football team.
If a student has a "C" average year round, and brings in cans or another form of charity, their grade should be bumped up no higher than a "B". Offering incentives might draw people who were not interested in donating at first. Proponents of true altruism, giving for the sake of doing the right thing, contend that the implications of donating only when there is a reward involved are deeply concerning, and portend the crumbling moral fabric of society.
I think that if some incentives help to gain charitable donations, then it is better than having less people to donate. In reality many people would not donate to charity as often if there were no incentives in it for them.