I was a taxi driver in LA - I've lived the past 10 years in Portland. One major difference in driving style (at least before a lot of New Yorkers moved to LA) is that in LA, people merged late in a fluid style, and traffic shuffled. In Portland, people line up a mile before the sign for the exit lane, and aggressively don't let anyone in. Which means you have to be extra aggressive to get in if you don't want to wait in a voluntary Soviet line behind a hundred idiots with two brain cells and nowhere to be. Thankfully, Portlanders are all passive-aggressive, and much less likely to get out and attack you than Angelenos.

Personally I always let people in when they need to go. What does that cost me? A second or two? When people actively try to cut you off from merging it leads to more accidents and more road rage. Just merge peacefully and let people merge without getting your ego involved. That's more or less how LA used to be, at least before a million New Yorkers moved there who didn't know how to drive.