The Simpsons is no different than Family Guy or American Dad or South Park. They make fun of everyone. I've never seen an episode of any of those shows that was strongly pro or anti.
They are all anti gun.
I don't watch much of any, but used to watch the simpsons quite a bit.
There is a few simpson episodes where they are strongly anti.
In both the Simpsons and a family guy episode they go forward in time and strict gun control laws are one of the things that made it such a great future.
Family guy is extremely liberal. One thing I have noticed with most comedy is that it is liberal, especialy the type of comedy that is centered on putting others down or making fun of things.
Two family guy episodes I saw were strictly anti gun, and I rarely have watched it or seen many episodes.
One had the neighbor in a wheelchair accidently shoot his gun and hit someone, and then made a statement you often hear from pro gun people about it being his right as an American to keep and bear arms, and own the gun he just killed someone with by mistake in a patriotic tone. It was clearly mocking gun ownership, implying that such a right is foolish and leads to tragedy.
Another one had the dad Peter go back in time with Death to when he is 18 and change the past. When they go back to the future the world is a great place, but he no longer is married to his wife. They tell him the world is a great place, and while talking with the dog one of the cited main reasons is strict gun control. The dog (who is made out to be the smart intelligent one, much as Lisa in the Sompsons) is telling him he should just let things be because the world is such a better place, and strict gun control is one of the main reasons for the wonderful present. He goes back in time and undoes it all to get his wife, ruining the future as well.
A simpson episode had a similar theme. It is Lisa that comments that the world is great and one of the main reasons is the implemented strict gun control. She shows a pro gun control stance in several episodes and is clearly made out to be the intelligent smart one in the family. This implies that her opinion is usualy the most logical. So when she expresses a desire to ban or restrict guns, and gives a logic to support it in many episodes it shows that the writers are likely anti gun.
This is a main reason cited among a mere handful of reasons in both shows when they go through time and go to a perfect future. The message is clear: One of the ways to reach a peaceful happy future is with strict gun control.
Actualy here is the family guy episode he goes back in time and when he goes back to the future, things are great with one of the main reasons being gun control. It is titled "Meet the Quagmires"
http://www.imdb.com/title/tt0945076/
I will try to find the simpson's one, but there is so many listed Simpson episodes. Appearantly all the family guy episodes can fit on a single page so it was easy to browse the episodes.
The head guy Matt Groening of the Simpsons is very anti gun. The Homer gets a gun episode is the first one with a different producer and had unique influances that helped give it a more neutral slant on guns than in standard episodes.