I can see why you would need 15 rep to upvote, and more to downvote. I do know that handing out upvotes to everything from a particular user, no matter how much you like them or how good a particular question or answer from them was, is considered an abuse of the system and will get the votes deleted. It's more obvious how downvotes can be abused. And the main purpose of this site is to ask and answer questions.
That being said, I do like to give credit where it is due, and give especially new users the rep they deserve for good questions and answers. But at some point, I wonder if going around sprinkling upvotes like candy indiscriminately, even to deserving answers, if already handsomely rewarded, would be going too far. I guess I don't like cheap upvotes to marginally deserving answers of mine either, and they can mask what I'm doing right to earn the upvotes.
The most glaring example of this potential altruistic "abuse" would be someone with barely 15 rep jumping on the chance to upvote, if altruistically to help others like themself along who are happy to have so much as 15 rep (each upvote to a question gets them 5/14 and an answer 5/7 of the way there!) and forgetting about asking and answering questions of their own (perhaps out of shyness from a few early downvotes.)
At what point do the angels that hand out upvotes and reputation, however deservingly, go off the deep end into sin by overdoing their gifts?