Knowing if you used it you'd swing would be a deterrent for anyone who picks up a knife as they leave the house.There are truly very few terrible things done in the UK today by people who are in a reflective mood. Mostly, they happen in moments of poor emotional control and without any deliberation whatsoever.
I doubt any of the young men who stick knives in each other over gang turf wars think seriously about consequences when it comes down to that 'him or me' moment.
Which is why in the 50s, despite a lot of 'bring back' bayonets, pistols etc, the teds and other thugs used straight razors, boke chains etc. Because even IF somebody died, they wouldn't necessarily swing. Having a weapon of war, and using it, was a guaranteed rope dance.