It's not a shipping wallpaper. I wanted to join in the community project because some of the comments I had received from other deviants were hurtful and full of bash-ness. I also wanted to support the LGBT community, which is what this day is all about: accepting the LGBT community and appreciating others. And why should you care? There will be someone that will bully you in different places, even here in the internet.
One more thing: why should you be offended in a MLP:FiM episode about bullying (anti-bullying, to be specific?) It's an important issue that parents want to talk about to their children. It's a special episode to the target demographic and us bronies, and should give some people that have never heard of this topic an insight of what it's like.
Lastly, if I didn't explain it carefully, then I sincerely apologize for not doing so.