The big deal is that some people don't want to see sexualized ponies, which is exactly what all versions of that pic are. You say some people are just so oversensitive to it, which is subjective, in the same regard as it can be said you're just so desensitized to it. It's all just subjective. Here's some things that aren't, however.
FACT: Some people don't like it. Now whether or not they should is subjective, but the fact that they don't is not. Now this doesn't really mean much, as a lot of people don't like a lot of things, but when coupled with...
FACT: At least one mod didn't like the picture, or at least agreed that it was violating site posting rules. The claims that the other side is just oversensitive stops holding water at this point.
FACT: The picture in question was removed for, once again, violating site posting rules. This is more of a second part to the previous fact, but it's important. You believe that there is nothing wrong with the picture. Fine. Other people, apparently including a mod, disagree, and it was removed for violating the rules. This is not clopper's corner, it is the TF2 modding thread on the /g/ board of Ponychan, and the picture has been deemed inappropriate for the site. If y'all are really hard up to talk about it, might I suggest making a steam group or something for it, because it has no place on this site, *insert Wonka video*. Now might I suggest dropping the discussion, or even more prudent, stop degenerating to nothing more than a parasprite and describing the inappropriate picture to people you know are bothered by it. It's an incredibly dick move.
And don't get me wrong, I'm not a prude. It's not the what, it's the who. I don't like sexualized ponies. I'm the same way with Krystal from Star Fox, who happens to be my favourite video game character for non-sexual reasons. It's the who that makes it physically nauseating. You say it's being oversensitive, but I doubt you'd say the same about somepony not wanting to see a porno starring their mother, much the same way I imagine you'd really not want to see a porno starring your mother, and would probably be really upset by it. It's the same principal. There's people that don't want to see it, and bottom line is, there's rules put in that if people follow means they shouldn't see it.