Perhaps I’ve missed something about Russian law, but it seems to me that it’s a conveniently trumped up charge to keep the women sequestered until (hopefully for the Putin Administration, at least) the attention blows over and the perpetually-distracted news cycle moves on. In short, I can’t imagine, at least from my cultural context, that such a sentence could be justified as anything less than government bullying.
As for the location of their “Punk Prayer” at the altar of a Russian Orthodox church, this state church has been in the pocket of the government for quite a long time, it turns out. In reading up a little more, the choice of such a church for their protest seems less shocking and more concertedly poignant, given the church’s complicity in promoting the agenda of the Powers that Be. Rather than standing up in the face of authority as an advocate for the poor and oppressed (arguably one of the principal responsibilities of a church), they have joined in the subjugation of human rights in Russia.