I'm still baffled by this thread.
My son is autistic and although he's not one to lash out he doesn't like unfamiliar kids getting too close and actually seems very wary of small babies. So I stay fairly close to him at things like soft plays, playgrounds etc, just in case. We gave up on play groups long before he turned 3.
But if a small, crawling baby approached him I'd gently remind him "she's just a baby, nothing scary" and we'd move along if he was uncomfortable. I would say to the mum, "it's ok he just needs some space" then probably say something nice about her baby. Just to reiterate - I would say something directly to the mum, not send a passive aggressive message via a crawling baby doing normal crawling baby things.
People are being deliberately obtuse here - pretending "no thank you" can't possibly be said in a sharp or clearly unkind tone or not getting that passing a message on via a baby instead of just talking normally to the parent isn't passive aggressive and actually quite ridiculous.
Likening this, quite frankly normal, absolute none incident, to adults forcing a hug or older kids pushing and stealing things are stretching the narrative just as much as the op is by her extremely sensitive reaction saying it's "cruelty".
They say there's a loneliness epidemic around these days. You hear all the time how lonely parents are. Maybe a good start would be talking to other parents in a pleasant way, instead of spending PLAY GROUPS anxiously Maintaining Boundaries, or avoiding places altogether for worry about "other snotty brats" interacting with our children.