I had the same problem UNTIL I found the custom targeting filters that aren't enabled by default. If I hit left shoulder button + B the targeting filter changes to "Enemies" (it's written on the screen) and now the left right targeting will only select things to kill. I also use it in FATE on my healer to cycle only through players so I can toss some heals out of my group, Left shoulder + X. It's awkward at first but its sooo useful once you get the handle on it.
