They said the "genetic integrity" line AFTER Voyager had invaded their realm. Given we didn't see much of their culture, that could easily be the equivalent of, "you have violated the sacred soil of my homeland." It doesn't mean an invader's foot is harming the physical soil, but an expression that the defender is going to fight for their home. I'd say they have every right to be POed about Voyager's involvement against them from day one. For all they knew the whole galaxy was against them, certainly Voyager was or appeared to be cooperating with the Borg and hostile towards them in every encounter. The only thing 8472 is guilty of, is having the audacity to hit back when attacked.