> Why not ask for permission instead of objection?

Because in most cases it was never my intention to photograph a stranger - they imposed this into the conversation by contacting me - most of the time I’m taking pictures of a lovely park, or a nice flower arrangement, or the broken beer glasses in the street after Carnival - and it is only after being interrupted that I offer the option. I certainly do not take photographs of random strangers unless it somehow captures the idyl of the scene, usually.

And in many cases actually, the conversation starts off irritable but ends quite friendly, especially if the photo is a good one and the person changes their mind and wants a copy.

It is possible to pivot from annoyance to friendliness. Especially if one understands the laws and the reasoning behind them. Ask for forgiveness, not permission.