I don't think that bringing a megaphone to an event to shout down other people is a legitimate form of protest. You want to protest: great, have a (legally cleared) demonstration in some different place. Hold your own event about how Singer is terrible. Write critical essays on the Internet. Crashing events with a megaphone is not "peaceful protest," it is hooliganism.
I think that the tactics of disruptive protest (blocking traffic, bringing a megaphone, handcuffing yourself to a tree, obstructing the entrance to a business) are sometimes justified. For example, I think they were justified during the civil rights movement. Disruptive protest has a lot of drawbacks: sometimes it turns the public against you, it often results in police escalation, if not very carefully executed it can endanger innocent lives and it usually imposes costs on random uninvolved people. But those costs are not infinite; it’s simply not true that there’s nothing I would trade them off against. Some injustices are really bad, bad enough that those costs are worth it if the disruptive protest works to fix them, and I do think that disruptive protests sometimes work.
I also think that a categorical rule against using violence to achieve political goals is necessary because otherwise people who just want license to commit violence will gravitate towards any movement offering such license. I don’t think a categorical rule against disruptive protest serves the same purposes.
And I think declaring that disruptive protest ‘is not peaceful protest’ is a terrible idea. Yes, it is. Crashing an event with a megaphone does not injure people or put them in fear for their lives. Please let’s not lead the fight against violent protests by trying to narrow what counts as nonviolent. If you think the protest was harmful, or that the costs to free discussion and free association were higher than justified by the benefits of the tactics used, by all means say that. I’ll even agree with you. The fact that a tactic is peaceful doesn’t mean that it’s wise or justified. But similarly, the fact a tactic is unwise or unjustified doesn’t mean it’s not peaceful protest.
“Some injustices are really bad, bad enough that those costs are worth it if the disruptive protest works to fix them, and I do think that disruptive protests sometimes work.”
Well, yeah, but this is the actual hard part. Once you’re at this juncture, you’re trading off between huge hard-to-measure utility sinks on both sides of the issue – “this Big Social Change would be a colossal good!” on the one hand, “your protest is only a tiny drop in the bucket of achieving that change!” AND “your disruptive protest is eroding the norms of our civil society by some unknown amount!” on the other – and of course people are going to overweight the priorities that are personally salient to them, and what you end up with is “politics.”
Disruption isn’t always a hugely costly problem, to be sure. But then physical violence isn’t absolutely always a hugely costly problem either, and there are Really Good Things that could probably be achieved by such means, and yet the calculus is such that we’re probably very wise to have broad sweeping rules against violence. It may well be that the calculus works out differently when you’re talking about issues like “can I drown out my opponent’s words with a vuvuzela?” – but just gesturing at the potential for Big Social Changes to be attained that way doesn’t get you very far.