I doubt that it's anything to do with NPO being "ebil", just that he's been opposing and fighting them for so long that he has no desire to be allies. From what I understand, there was debate about it, it was decided to hold off for a while. Then all of a sudden here we are - it's announced on the forums before it is on our own. Was there a vote for it? I don't remember there being one. Sure, the majority of the alliance, going by what was on that first debate, would likely have voted for the alliance, but at least the option to vote would have been nice.
Now looking around the forums I can see other rather interesting treaties being looked at, and I doubt we'll get the chance to vote for that, either. So, I can see where Blacky is coming from. And also, not very nice behaviour, Ventus. It's "you're with us or you're against us", is it?