I don't personally consider their actions a justification for why erecting the mosque is tasteless, primarily on the basis that the location and activity within the mosque/community center is not promoting terrorism. You can disagree with that, but it won't change my mind unless you can prove that the purpose of this mosque is to deliberately promoting terrorism.
You can also feel that it is tasteless on the basis of the events of 9/11 or the Imam's controversial statements, but I personally wouldn't. It's just fine and dandy with me if a similar event to 9/11 happened in my city and a religious building was later erected by the religious faction that those extremists came from - whether they were islamic extremists, christian extremists, judaic extremists, taoist extremists, buddhist or hindu extremists.
Of course, this flies in the face of the almost-koran burning, which is undeniably an aggressive attempt at creating discord. Every sane person already acknowledged that that act would be uncontroversially tasteless.