Antagonistic toward whom? It's a fact that Valve hired IceFrog, apparently thinking it an acquisition of DotA (like they did with Counter-Strike, Team Fortress, etc.). It's also a fact that IceFrog was neither the original creator of DotA (Eul was) nor the person who elevated it from a merely very popular mod to a worldwide sensation (Steve Feak was[1]). So it's always seemed to me that Valve skipped their due diligence on IceFrog -- otherwise why hire him? He didn't create DotA, was only tangentially responsible for its success, and doesn't own it[2]. On the other hand, he brings with him the good will of the community and a claim to the DOTA trademark based on use, regardless of whether the underlying IP belongs to him.

Thus, Valve's decision to hire him has always puzzled me[3]. Did they do it simply because of his claim on the trademark and his relationship with the DotA community? I have no idea. Based on this article, it seems there's at least one other possibility: they were too trusting and didn't have the organizational infrastructure to do a thorough background check (and possibly still don't realize where IceFrog stands in the history of DotA development). We'll never know what Valve's real motivation was, but I[4] at least have lost a fair bit of respect for them since this whole thing started.

Edit: I agree with you that neither Blizzard nor Valve should have the trademark. Ideally I'd like to see it ruled generic.

1. For all that it matters at this point, Feak did this without Eul's permission, and has profited enormously from infringing Eul's work.

2. Though trademarks are different from other forms of IP and it's not impossible that Valve will end up with the mark anyway. But regardless of who owns the mark, the characters and such in DotA aren't IceFrog's IP, and could be used by other people in other games.

3. This because, aside from these considerations, he's a not a great coder and has no art or other skills. So Valve can't have hired him for technical expertise. If he was a superstar developer I'd happily chalk it up to that.

4. Disclosure: I was heavily involved in the Warcraft III modding community from before the original DotA up to the release of StarCraft II. I watched this all play out in real-time, which absolutely colors my take on it.