It was arguably non-consensual in the book too, but we're seeing it from Jaime's POV, and he's fresh from a year of hell and returning to his long term partner and lover whose resistance, in terms of what she says, is 'not here, bad timing'. Had it been Cersei's POV in the books I suspect it would have come off differently but considering her very adulterous late husband used to periodically violently rape her, and that no one would have viewed that as rape by him, its hard to imagine her being much more vocal in her objections to Jaime either. That scene, in the book, is left open to interpretation but the episode was pretty cut and dry.

I think they did it that way for the same reason they played a lot of the characters nastier. A lot of fans have been forgetting that Jaime is an absolute bastard because he had what seemed a redemption arc going on in season 3, and oh isn't the Hound and Arya cute, and Tywin is cool and Lady Olenna, etc. The episode reminded us the hound is a bastard, that Jaime is a bastard, that Ygritte is a homicidal bitch, that Tywin didn't even wait for the body of his grandson to get cold before using him as an object lesson to his younger bother and mother with zero subtlety or sympathy. Margery is shown to be fairly indifferent to the deaths of either of her husbands beyond the inconvenience it caused her and you'd think she'd have a bit for Renly even if just and her brother's mentor and lover. Though I don't think the TV show ever mentions Loras was Renly's squire. Stannis's behavior toward Davos is beyond cold to nearly sadistic, very un-Stannis IMO, and Ygritte is never shown as sympathetic toward the kid whose family and neighbors she helps butcher when the Magnar is cheerfully telling the kid he's going to eat his parents, not even a 'that's enough' type remark. And we get the reminder that the Watch is composed of scoundrels. Dany was even a bit over the top, and I'm rather looking forward to seeing if the show will try to whitewash the aDwD incompetence or play it up less subtlety.

The book and show does try to emphasize that things aren't very black and white and that the shades of gray tend to be pretty black so I'm kind of happy the show took the time to remind everyone that the characters many are sympathizing with just because they get a lot of screen time and aren't total bastards on whim are actually still SOBs.