From what I've observed, the vast majority of car trips in my city could be easily replaced with a bicycle trip.
We would most certainly notice if the modest bicycle traffic in our city was replaced with car trips. The already terrible traffic would be significantly worse. "Stealing" some space for cars for a drastically more efficient means of transportation that's also 5-6 times faster than walking is a huge win both for people who want to get places reliably and on time and those of you who are always carrying cargo or can't cycle for some reason.
You wouldn't hear from me at all if it weren't for accusations like "stealing" space from cars (who in turn stole entire walkable city centers and streetcar lines!) and just made a little room for those of us who are able (which is most people!) to choose a healthy, efficient, humane form of transportation instead of hauling a 3 ton steel caged air-conditioned living room with armchairs and sofa on every trip.