Why blame Kamtza?
For the audience sophisticated enough to already be familiar with the basic story of Kamtza and Bar Kamtza, I would like to share here a point from the sefer Netzach Yisrael by the Maharal (credit to my husband, Rabbi Brown, for pointing it out to me). The question is why is the account named for Kamtza and Bar Kamtza? Kamtza is not even present in the story. He was on the guest list, but did not even show up to the feast because his invitation was delviered to Bar Kamtza by mistake. So why should his name be connected with the event that is pointed to as the cause of the churban?
The Maharal explains that when sinas chinam dominates, even the love of friendship becomes corrupted as a means to divisiveness and exclusion. The "love" that the host of the feast had "for Kamtza was in truth chiluk vepirud umachlokes kemo hasina [division and separation and dissension tantamount to hatred]. It was a means to division -- a group of intimates formed for the sake of excluding others. The name of Kamtza refers to separation, for its root refers to kemitza [removal] as in "vekamatz misham" (Vayikra 2:2) "That which is separated and removed from everything is call kmitza." Thus the name of Kamtza signifies that even the relationship of friends was corrupted into a manifestation of separation rather than of love when sinas chinam dominates. That is key point in bringing about the churban. The application to a society prone to cliques and strongly defined social circles should be obvious.