Comment 3 for bug 231060

dnsmasq is a general purpose dns (and DHCP, but let's ignore this for the purpose of this conversation) server.
The dnsmasq package installs itself and starts listening on all interfaces. That seems like a reasonable default behaviour for a general purpose caching dns server to me.
libvirt uses dnsmasq (the binary, not the service) to provide dns and dhcp services to virtual networks. If you're installing dnsmasq and libvirt-bin alongside each other, you have to work out the conflicts yourself. I'm not convinced there is a reasonable default fix for this case.