MIL said I need to let my son cry himself to sleep 🙄

I can't stand her as it is..but I explained to her how I was tired & that it's been hard to get some things done because my son hasn't been a good napper lately. And she says "well, why can't you just put him in his crib and let him cry himself to sleep?" like it was the most normal, innocent question she's ever asked. I personally will never do this..although I'm sure others are fine with it. All I could think to say was "yeah, I'm not doing that.." and changed the subject. Why can't these older generations drop their outdated bullshit already!? Rant over.