MT,
Hypothetically speaking, if he felt that she had taken advantage of a captive audience then I suppose he felt that he had an equal right to give voice to his indignation.
Normally, I would agree with you that heckling is rude and infringes on the right of the audience to hear a speaker or performer.....but can you honestly say that it is NEVER justified?
I don't know what the guy said, specifically, but I'll wager that he didn't feel compelled to speak out until Streisand started her political rant.
The arrogance and temerity of subjecting ticket buyers at a concert to one's personal political views, in a setting where those who might voice objections can be summarily ejected, is becoming all too common a trait of Hollywood's elite.
Regards, Shuckins