Making generalizations about people is a problem when the generalization is false or misleading, or is being used to make a false or misleading argument, which is often the case. If you’re wondering if a given generalization is problematic, odds are the answer is ‘yes’ otherwise you probably wouldn’t think of it as a generalization.
Memes are reposts! That’s their defining characteristic! They become memes by being reposted! If they didn’t get reposted, they would not be memes!