Biking is as common in the Netherlands as high winds and rain. I ride in the rain all the time. You wear a jacket. Same with cold, except you wear a bigger jacket. Biking in the snow is common in Finland. I've biked in freezing rain. It's not always super pleasant, but is a small amount of discomfort really worth destroying our cities and our planet to prevent?

I don't have a great answer for heat since it's not something we deal with here (as much). Cycling requires less energy than walking, so if you're not biking hard you can keep as cool or cooler than walking. Where mass transit exists, use that if you really need to get around... And, honestly, you should generally stay inside during dangerous heat anyway.

Kids, pets, and elderly folks regularly die in cars during normal summers. Things are only going to get hotter and we're going to need to adapt our culture around that.