I think I was able to get out of the .NET loop. Here's how I did it:
1) When it prompted to repair/remove the VS2010 redistributable, I hit cancel. It went on to the .NET framework.
2) When the .NET framework finished, I clicked "restart later"
3) This brought me back to the Steam "first time setup" window. I clicked "Play game"
4) It brought back the VS2010 redist prompt, which I cancelled again
5) It ran through the .NET framework again, and this time the BL2 setup program opened.
6) I closed BL2 and re-launched it from Steam
7) This time I did "repair" on the VS2010 framework
Now I can launch BL2 from Steam w/o any prompts.
YMMV.