Spam is like a car. I like that ONE CAR over there. You can call that car spam. You do not like that car. You might like this other car. But I might call the car you like spam. This is very subjective. Other people can upvote posts and comments that they say are great and not spam. But others may disagree and claim they are upvoting spam. Those first people can argue and say they are upvoting stuff they like.
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For example, I can upvote Pro-Trump stuff. Other people might say that is spam. They may upvote Obama stuff and I might look at the anti-Trump stuff and call it spam. So, is it spam because I do not like it?