The challenge is an interesting exercise, and I will try to think up some examples, but your comment also contains an implied accusation which I'd like to respond to first.

By my count, this post includes critiques of four weak right-wing arguments (abortion, euthanasia, taxation, affirmative action) and three weak left-wing arguments (eugenics, sexism, capital punishment). As far as I know, neither side thinks MLK was a criminal. That means I'm 4-3, ie as balanced as it's mathematically possible to get while seven remains an odd number.

And I think the responses I see below justify my choice of examples. Shminux says the pro-choice converse of "abortion is murder" would be "forced pregnancy is slavery"; TGM suggests below it "denying euthanasia is torture". These would be excellent examples of TWAITW if anyone ever asserted them which as far as I know no one ever has. Meanwhile, I continue to walk past signs saying "Abortion Is Murder!" on my way to work every day. I don't know who exactly it would be helping to give "Forced Pregnancy Is Slavery" equal billing with "Abortion Is Murder" here and let my readers conclude that I'm arguing against some fringe position irrelevant to the real world.

If you can think of left-wing WAITWs that are as well-known and catchy as "abortion is murder!", I will happily edit the post to include them (well, to include one of them; otherwise it'll be 5-4 and the leftists will start complaining). The best I can do at the moment is anti-war arguments that seem to equate for example humanitarian intervention in Rwanda with invading your next-door neighbor to steal their land because they're both "war", but that one doesn't come in convenient slogan form as far as I know.