Politics is rife with the possibility people will be emotive 'about you/them/their/issues'. Even our media is capable of whipping themselves up into a frenzy, (ie Alan Jones calling for "Julia Gillard should be thrown out to sea in a chaff bag").
History tells us attacks on public figures are nothing unique, (of course we do not condone them).
Crowd behaviour can be complex, it's not specific to one group, it can be about war, economies, gender issues, taxes, animal/human rights issues, take your pick of what people can, and do protest about.
Many of us think the general 'behaviour' was unnecessary, you are talking about a crowd behaviour, it could have come from any person(s), any creed(s), color, economic situation.
Julia Gillard and Tony Abbott will back at their work today, going about their business, often it is indeed a thankless business/vocation and can get nasty, they can be vilified and verbally abused-from 'anywhere/anyone'. Even on internet forums. I don't think somehow either Julia or Tony would be giving much thought today about the event/behaviour, wanting to just get on with their jobs.
Crowd protestors and human behaviour will continue to (at times), become extreme. I haven't done any extensive research about specifically Aussie protestor behaviour, but it does seem mostly responsible.