Causes (?) of Crime Rate Reduction

There are many interesting ideas (which might be right or wrong) about what caused crime rate reduction:

1. Fixing Broken Windows Effect: Fixing/preventing small crimes lead to fewer crimes in general. Criticism of the idea is here.

2. Legalized Abortion: Legal abortions lead to fewer unwanted babies, cutting down the number of criminals. Criticism here and here. However, in the extreme case, it's obvious that abortion does prevent crime--if there is no more baby, there will be no crime. :-D

3. Unleaded Fuel -> Less Crime: Presumably, lead turns people into idiots who commit more crimes. A paper can be found here.

It's interesting to note that abortion became legal in many US states around the same time that leaded fuel was banned.

If I have to bet which one is the most correct, I would bet on #3 more than on #2 and on #2 more than on #1.

I wonder what other toxic substances we are being exposed to will create problems in the coming decades.