I hate it when people say shit like this so authoritatively. Like this is some conjecture at best. It’s a baby. No one knows why a baby does this. Someone assumed that and some other people said oh yeah that makes sense.
It doesn't really seem that hard to test? Emotions--at least in their occurrence and strength--are detectable with non-invasive brain scans. We've been doing that for ages. Put some electrodes on a baby, let them see their mommy, watch the graph spike until they turn away.
The argument "how could we know that about babies?" was used, for decades, to justify doing surgery on babies without anesthesia. They can't talk, so who knows if they're feeling pain or not. Guess we can safely assume they don't. Point being, we don't have to have a conversation with them about it to know why they're doing something.
Oh yeah let me just plug in an fmri and find out if someone is definitively experiencing “joy”. That’s high level somewhat subjective emotion, not pain. Neurological understanding is not nearly as advanced as you think it is. I spent my post doc doing fmri research; the best thing you could come up with here is “areas of the brain associate with pleasure are highly activated” but even that doesn’t necessarily indicate the baby feels overwhelmed. Maybe I’m wrong and there’s some fancier neuroscientist out their that can read baby brains but I doubt it
While I think scanning baby brains is not really viable for this (see my other reply) they actually do basically put babies in a restraint for X-rays and neurological scans that looks pretty fucked up. But I mean if a baby is having seizures or has a suspected broken bone you have to get imaging, even if it’s kind of cruel