I get it: you need a splashy-controversial hook to grab the attention. It's just so ****ing lame that the Justice League is brainwashed to allow them the convenience of killing off heroes because you're right that it sets them up on a losing path out of the gate.
There's an infinitely more interesting premise in Waller discovering the League, a group of literal gods amongst men, are up to something that may or not be in humanity's best interest, so, in an approach that they're perceived as power-mad, she assembles a Suicide Squad to stop them by any means. I'm just shotgunning this idea from the hip so I don't have a thought to whether you can kill JL Members or not, but I love the idea of still being able to swap SS characters, but they get picked off (captured) one-by-one until just one remains to handle the finale.