Ukraine has an oligarch problem (with Putin at the head of it), not a Russia problem. Putin ultimately wants to exploit the resources of Ukraine unimpeded like he does in Russia - and he’s tried puppet governments, and the people fought back, so now he is trying force.

Ukraine killing Russian civilians (who are also victims of Putin’s greed) is not going to deter Putin. Putin cares about one person - himself - and everything else is only a means to enriching and protecting himself and his status. He only cares about Russian civilians to the extent that those civilians living is in his best interests.

So killing random Russian civilians is unlikely to achieve much except depriving some innocent family of some of its member. Targeting Putin and his property, oligarchs and generals is much more likely to make a real difference.