Sometimes they need to, such as in work environments.
Yes, and that's been the cause of more shenanigans than can even be imagined. There are many married women in the workplace who like the idea of gaining the attentions of men not their husbands. (And vice versa.) In modern society, marriage is seen as a serial thing anyway, and if someone sees an opportunity to "trade up", well...
Don't say it doesn't happen, because it does. And contraception (
a fortiori sterilization) gives a mischievous wife (or husband) the opportunity to make their spouse into a cuckold, with no one the wiser.