They are trying to stop people from orchestrating illegal events overseas and escaping US law because the acts weren't committed on US soil. These kinds of laws have been around since the 1970's (and probably even before).
It's easy to use this law as an example of big government, but as long as we're going to keep drugs illegal here it makes no sense to let US citizens facilitate drug operations outside the US.
Aside from the fact that they are:
1) Not breaking any laws in the US.
and
2) Not breaking any laws in the outside country.
So this is a fun Internet debating topic for closet liberals, but not very interesting outside of that context.
lol
If by "closet liberals" you mean "people that are against arresting folks for breaking absolutely no laws in the United States whatsoever" then you hit the nail right on the head.