I don't think Johnson and Spinnet are saying they want to kill every purist even if they're pissed. If we did, we'd have just knocked that building down on them. Likewise I think if there's an option for "only Death Eaters" compared to "Death Eaters with civilians" we all know which one we'd pick. We had an opportunity here to get some knocks in and we took it even if this wasn't some clean nice perfect victory.
They're always going to twist things. That's what they do to keep themselves looking good despite what they do. Maybe they say we attacked them and their purist friends and we're horrible. Well, we also showed the world that we're not just playing defense, either, and we can actually hit them back and keep them off kilter, and that's important too for when people start looking at us and thinking if we can actually do anything.