Yes it's allowed as of now but the issue is that making this the most upvoted thing in a few days sends the message that posting gif's is more desirable than actually discussing the game or posting game related content (commentary, montages, news, speculation, game discussion in general, etc.).

You might say something along the lines of: "It's a joke, what's the harm in a little fun?".

Already this sort of low effort, loosely related content is already taking hold this post is already rising fast to the top and is almost exactly the same thing posted less than 24 hours apart.

We as a community should consider banning links that aren't strictly halo related and anything else can be a self-post so that we can still have fun and jokes but remove the karma-whoring aspect that inevitably leads to the decay of any subreddit that gets even somewhat popular. I don't think that anyone here wants this subreddit to go the way of r/gaming.

Edit:

Of course the obvious question is, what defines what is "strictly Halo related"? My answer would be to either let the community decide (bad idea in my opinion because any community defined subreddit tends to be wildly off topic) or let the mods decide because they obviously care about the community and care about keeping this subreddit Halo focused.