I think a donation fee is ok. Its fair to give developer a share, and this way everyone donates proportional to their "income".
5% is not okay though because we have electricity to pay for too ...
Why not?!
A miner which gives you 2x the speed of regular one (if any!) and you think 5% is too much?
Don't use it then.
Its a win-win for the developer AND users. Until better way to reward devs is found