How would Roose possibly consider what Ramsay did irresponsible?
He admitted to Ramsay that he raped his mother to sire Ramsay. That he could see that this was in fact, his true son, no matter what. If anything, Roose would endorse marital rape.
And think back to the Tywin/Tyrion stuff in Season 3. Tywin put all kinds of pressure on Tyrion to rape Sansa on their wedding night. This is the normal expected behavior of wedding nights in Westeros. Why on earth would the culture that endorses this exact behavior think anything out of the ordinary happened?
You're showing a severe inability to understand the perspective of these characters, even though it has been quite well established in the show, not only the books.
And Sansa is not politically that powerful on her own. At least from the Bolton perspective. She has no allies known, no knights at her command, no access to wealth or the connections to use them. Hell, she's publicly been missing in action since the Purple Wedding.
She's important as a figurehead, and legitimizes the Bolton hold on the north. But a lord sleeping with his wife on their wedding night - which is how Roose and pretty much every Westerosi would see it, unless Sansa goes out into Winterfell square and convinces everyone otherwise against hundreds of years of "Bedding ceremony" tradition - will not be perceived as a slight against her. Hell, the Boltons are so fucked up, they'd probably think he was "doing her an honor" . . . much like how Roose said the only reason he didn't kill Ramsay's mother was that he knew she had carried his own child.
Just because you couldn't see the foreshadowing, the setup and the explanation of the character's psychology on the show doesn't mean that all of that isn't in the show. It is. Go and watch previous episodes. Sexual violence is a constant on Game of Thrones, either being alluded to, talked about directly, or simply shown to the viewer.
If that's distasteful to you, then fine. Don't watch the show. You're completely entitled to that opinion. But it's been in the show from the very first episode and to assume that it hasn't been, or that this event is somehow not EXACTLY how this would play out considering everything that's been set up is myopic.
If anything is going to lead to the demise of Roose and Ramsay, it's going to be a certain Stannis the Mannis marching his way to Winterfell now. Though I'm guessing we're about to see Sansa and Reek take more direct action in the next episodes considering how this last one ended, perhaps hastening things along, it won't be because of Sansa's nearly non-existent political clout.