The perfective and imperfective confuse me to no end. Why isn't it "porozmawiać" here?
Both can be put into this sentence. The meaning however will shift.
Musimy rozmawiać o przemocy. This implies that we should debate, draw conclusions. Maybe in many places, with different people, maybe many times. I thought who and when could say that and first what come to my head was: the studio of some TV programme with minister of education as guest, who says her (yeah education in Poland is dominated by women) meaningless speech blah blah.
If I would have to talk to a group of people like a teacher to the class I would go with 'musimy porozmawiać o'. The wife to the husband: Musimy porozmawiać o naszym synu. (We must talk about our son). Another example You must talk to each other, because it is dialogue that builds relationship. Musicie ze sobą rozmawiać, bo to dialog buduje związek.
Maybe it's not completely not suitable, but that sounds very perfective (we have to discuss it, now), and "rozmawiać" is imperfective (we have to talk more about this topic, pay more attention to it).