My buddy just gave me a phone call, saying he quit his job, and plans to use the money he has saved up to start filming girls, just like other adult websites. Now I know that the owners of the Adelita bar and Chicago Bar would send a leg breaker to stop this kind of shennanigans with their girls, but what else am I missing in terms of negatives?

I think you should look into the legal aspect of it.
I am not sure but filming porn in Mexico maybe a big
no no...  
tell your friend good luck.

While the simple act of prostitution is legal in Tijuana, almost anything a person does to make a buck off it is illegal.  (Only the chicas can legally make money.)  People talk and if you get caught you won't be happy.  Making prono films in Mexico is different thatn in the US.  They don't like it--as you'll find out if you're caught.

I Hope your buddy has lots of money because I too believe that filiming porn is illegal in Mexico.
But then again, so is drug trafficking...and you know how profitable that is.
For the right amount of money, you can do anything you want in Mexico.
If it were that easy, all the porn companies would be shooting in Mexico instead of in the San Fernando Valley.  
If your buddy grew up in Mexico, he would know the ins and outs but if he's a Gringo, well tell him that it was nice knowing him and wish him well...