here is no "should". There is only what people are willing to tolerate in public spaces.
We are free to assemble to counter-speak, speak back at them.
We are free to drown them out.
It's not a problem in public spaces. Nobody ever comes to hear them. Lol But there may be hundreds who come to counter them, drown them out.
The police should be enforcing hate speech in the streets, that's the law (yes I know they didn't in this case, & yes that's a bad problem).
But what if an alt-right group gets a permit to have an assembly in a public place, but they've never spoken legal "hate speech" before and aren't doing so during the event, but are saying some very controversial things, like we must lower annual immigration rates etc. Should protestors be free to drown them out with heckling etc.? Is that breaking the law by "disturbing the peace" etc since they have a permit? Is it harassment?