> If they have no place to put them, they won't have them
This is demonstrably false. People still need cars to get to where they need to go, like work, or their doctor's office, or the grocery store. There are no alternatives. Public transportation doesn't get them there. Ubering everywhere is more expensive than owning a car. Until alternatives exist, not having a car isn't an option.
If you've been to cities where there isn't enough street parking to meet demand you'd know that even when people have no place to park their cars they still keep cars. They just go to extremes to find/keep/make parking wherever and whenever they can and often have to spend long periods of time driving on streets/circling blocks to find a spot. They block traffic to wait for someone they think might be leaving soon, they walk great distances to get from where to park to where they need to be, they park in illegal or dangerous places.
There are many negative consequences to this behavior which impact everyone around them, but people can't help but do it because they're left with no alternatives. Examples of this abound. I've seen statistics like 30% of all traffic in urban areas are just people looking for places to park. (some studies have found that number to be as high as 75%!) or that the average amount of time drivers spend per year looking for place to park is 17 hours!
> No, having parking requirements should be done selectively, if at all.
That means the same thing.
> If there is sufficient market demand, the requirements will be unnecessary to get developers to include them
That's not how markets work. If it will make developers more money to not give people the amount of parking they need, then developers will not give people enough parking. All other negative externalities be damned. None of it means there will be fewer cars on the road.