If you think that there is a distinct group of people who commit all the crimes (as was suggested), and we can solve the problem of crime by locking all of them up, than you are mistaken. Or rather, that group is "everyone."

It's an easy trap to fall into for two reasons. It would appear that you and those you know aren't capable of being criminals. This is more comforting than it is true. Everyone, including good people, has the potential to do something horrible; the problem of evil isn't that it's present in a certain group who we can imprison, the problem is that it's present in us all.

The second thing which makes "lock them all up" a seductive proposal is that it's cynical. Cynicism can feel like the opposite of naivete, so it can feel like you're being clear eyed and realistic about the situation and that the people you disagree with (say, prison abolitionists) are naive bleeding hearts. But cynicism is actually just another form of naivete. It's making the same error - blinking while staring into the abyss - with different aesthetics.

> Then I should be imprisoned if I present a threat to the public.

The problem with this is that's it is extremely easy for people to define "threat" in ways that are convenient to them or that support their prejudices, a la Reefer Madness.