I don't understand why people get upset by reposts.
An essential element of memes is how they spread across the internet on different sites. When someone says they like memes but don't like reposts, it sounds to me like someone saying they like Chinese food, but don't like rice. It doesn't fit.
I've tried to figure out why people get upset about it. I think some people really think there is some value to memes being original. They work hard to be creative and make up new memes that haven't been done before. So for them, it's probably frustrating to see a meme they've seen before getting upvoted. I think they may not really be upset at the person reposting so much, but are indignant that people would upvote it. Maybe that's why they don't say something until it hits the front page (either that, or it's just that they didn't notice it until then).
There's a lot of different views out there on it, I guess. :)