Nice post. I agree almost entirely with you, but you can't put a bollard everywhere, and even if you could, bad people would find a way around or between the bollards, or simply another way to hurt people. It would be like playing a futile game of whack-a-mole.
At the end of the day, there are people who are so mean-spirited that they want to hurt innocent people for no reason, and they will find a way to do that no matter what we do. Honestly I think a lot of it is mental health more than anything we can really protect against.
It's not possible to wrap everyone in cotton wool, and in order to have some freedom we risk a small percentage of harm. There is no way around that. Without that freedom, there's also the IMO much larger risk of harm from the authorities themselves.
There's no way around it, living in the world involves some risk. It's unrealistic to not accept that risk and fantasize that all outcomes are preventable.
Like another comment mentioned, there are literally tens of thousands of stabbings in the UK every year. Why are we even talking about removing fundamental freedoms (the right to privacy) in order to probably not prevent a few unfortunate deaths per year? The payoff is so small and the cost is much too great.