I'm not sure what you would call them, but you wouldn't call them "critical thinkers."

Because a critical thinker would have their own thoughts about links they wanted to share. They would be willing to discuss why they thought a link was important, and the issues they thought it touched on.

People like this seem to live with very little skepticism. I read a lot of news sources where I feel I can trust them on certain issues and not on others. I can trust the New York Times on a lot of things, but I also know that they tend to cater to a more wealthy audience and that their foreign policy ideology clashes with my own. That doesn't mean they only peddle warmongering class-war bullshit, although they do produce a lot of that. They do also produce a lot of solid, thoughtful reporting, but it still requires skepticism on my part in reading those articles and not just taking them as "gospel."

A meme is too short and simple to really get into complex ideas, and as such, memes are good for sharing simple, accessible ideas, but very bad for sharing more complex themes. Once again, lack of skepticism and favoring simple ideas as opposed to understanding the complexity of the world requires more complex understanding of it.