Bet they wanted to though, 99.9% of that audience were probably thinking the same as the person who threw the bottle but had the good sense and respect not to, there's always going to be that .01 percentage though, unfortunately.
There used to be a few punk bands that would go batsh*t crazy an jump in as the slam dance turns melee (as in, willfully fomenting and joining a riot and fighting for sh*ts and giggles).
As for the bottle throwing incidences (at least where they affect artists that I either like or am paying to see perform live) I am confused as to 1) why do it (I know drugs and alcohol are probably at the heart of 99% of these)? and 2) why don't the lousy c*nts (who presumably paid for their tickets), standing around the bad apple, beat the piss out of him?