In any way it might be applicable, really... "Viral" not really describing any particular notion involved in the tendency, but the velocity and means of its spreading. That's part of what makes its proliferation so difficult to pin down.
A phenomenon I've noticed spreading in nearly viral fashion is an au courant total denigration of the notion that people matter - a notion deeply held that human disposability is something to be constantly if tacitly celebrated as a given virtue. It would be trendy cynicism if it were flippant...