You’re absolutely right that it is a difficult question where to draw the line. Different countries will do it differently according to their devotion to individual freedoms vs communal welfare.

The knife (as opposed to sword) example is interesting. In the U.K. you’re not allowed to sell them to children. We recognise that there is individual responsibility at play, and children might not be responsible enough to buy them, given the possible harms. Does this totally solve their use in violent crime? No. But if your alternative is “it’s up to the individuals to be responsible”, well, that clearly doesn’t work, because some people are not responsible. At a certain point, if your job is to reduce harm in the population, you look for where you can have a greater impact than just hoping every individual follows the law, because they clearly don’t. And you try things even if they don’t totally solve the problem.

And indeed, the same problem in software.

As for the violent crime rates in the U.K., I don’t have those stats to hand. But murder is at a 50 year low. And since our post-Dunblane gun laws, we haven’t had any school shootings. Most Britons are happy with that bargain.