I think it is completely backwards that anyone would ever think them cruel. They can and do save lives. And I say that as someone who isn't that keen on them personally.
I think my aversion comes front the fact they seem so overused here (**disclaimer, I know most mothers use them sensibly and teach road safety with just using the reins as extra security JUST IN CASE... So this this just what I have seen here and not a claim all mothers are like this... At all). Like I will see toddlers Fins age now pulling their parents along by them, not holding hands to cross roads, being held back from constantly running off with them, being held up by them while having a floppy tantrum etc. I've seen children arrive at a play park, be released and literally bolt and run straight away as soon as they are unclipped.
I've been to a farm park, which was completely child safe in the petting fields, and been the ONLY parent there with a toddler walking free. All the others on open grass with no roads or falls or hazards anywhere close by... On reins. Being stopped from running, playing, exploring, experiencing what takes THEIR interest etc in what is probably THE safest place to do so. If you can't let your toddler run free in a field then when the heck can you? Incidentally despite there being big signs up to pet and feed the animals by picking weeds etc from the wildgrass area AND hand washing places signposted AND sanitizer avail regularly... All the children were being prevented from going anywhere near an animal (in pens)... All being told they will bite or give germs. Fin was there in his wellies, tramping about, going up to whatever he wanted to experience at that moment, picking clover flowers and hand feeding the goats with such glee and it just felt so odd that all of these other kids were being kept from experiencing things the same.
I've been at a play park and seen a toddler on the swings... With one parent pushing and the other holding the strap from the little life backpack. That made no sense. The same parents held it when the kid went on EVERYTHING. I get hovering, I really do. But surely holding a rein tight while your toddler goes down a pretty small slide is creating more risk than what it could possibly prevent?
So, to conclude. They are absolutely NOT cruel. We do not use them, but that was a personal choice and as a SAHM I did have the time on every walk to wait while he sniffed every flower and picked up every stick etc and to turn around and go home if he refused to hold my hand or listen etc. If I had places to be, had to get us to nursery etc with a deadline etc, maybe I would have used them too. It could have also have been that we lucked out with Fin and that Amelia is too strong headed to use the same approach with when I need to have my eyes on too. Maybe I will need one for her at she point. I will never rule them out, they absolutely have their place and can be wonderful... But certainly here they seem to be overused. Sometimes it does seem that using reins has been done instead of tackling behaviour issues head on. Sometimes it seems they have been used in a way that the child hasn't learnt boundaries or road safety and when let off them they are at real risk of just running out into a road unaware of the risk as it has never been taught. Sometimes kids seem to be in them when there truly seems no need to be.
Some people mis-use them as they can so many other tools and things and that is a bad thing. But they are still not at all cruel. Xx