I want my children to be able to swim because I don't want them marring our holidays by refusing to go anywhere near the sea or a swimming pool/only going near them if I put them in armbands and hold them the whole time (too many children, not enough arms).... and also don't want to lie if I take them canoeing at a canoe-hire centre that they can swim when they can't.
I want them to learn to swim so that they can in later years choose to do other water-related activities that I would be terrified of allowing them to do if they couldn't actually swim - if they want to. If they don't, they still haven't lost anything learning to swim.
I also want them to learn to swim because they are both extremely hypermobile and swimming is an extremely effective form of exercise for people who need to be careful about the amount of stress they put on their joints, but who need some way of safely building up muscle strength and getting cardiovascular exercise.
I also want them to learn to swim because I don't want them to feel scared around water and don't want to feel scared taking them near water - I don't care whether it's rational to feel scared or not, or how likely they actually are to drown, I just don't like standing near the water's edge with a child who panics when they get a wet face, let alone when they fall in altogether. And I don't like imagining some little boy or girl pushing them into the water for fun one day, because they don't realise they can't swim.
I also want them to learn to swim so that they don't get teased for not being able to swim.
I also want them to learn to swim so that they aren't angry with me when they are adults for being too lazy to bother to teach them (as a couple of my friends are with their parents, who had to have lessons as adults because they felt they were missing out on a lot of activities because of their fear of being on or in water as a result of never having learnt to swim or been taken to swimming pools).
I also want them to learn to swim because I think swimming is fun and want to share something that I enjoy and makes me feel good about myself with my children.
I also want them to learn to swim so that they never need to feel excluded from friends' activities just because they can't do something many other children can. Same applies to riding a bike - it's good exercise, a useful skill, a lot of people enjoy doing it, it can get you to work cheaply (unlike swimming, except, possibly in very rare instances!!!) and it's something it's embarrassing to admit you can't do...
I think that's more than enough reasons to think I should make an effort to teach my children to swim. I don't think children need to be water babies from a very young age, though - not all children can be. I took mine to swimming pools from when they were very young and tried group and then individual swimming lessons, but this hasn't resulted in them being early and confident swimmers - they have taken their own time and are only in the last few months becoming quite competent and beginning actively to enjoy learning, rather than preferring to splash about. Some need longer than others to learn and some children enjoy it more than others.