[TheChad]

read OP, rest tl;dr

It really depends on two things for me. A - who is on my left; B - how the game is. B>A too.

B
If it is a super juicy game, I prob won't worry too much about the player on my direct left most of the time (in fact, I'll be MORE inclined to call his raises with trash than if the game is tough). If the game is pretty tough, then I'll put a little more stock into my position on the flop.

A
If it is a meh game, then this really depends on the player to my left. For a while, I'll play tighter PF than normal until I can pick up a read and adjust.

I really have no problem calling a raise from the SB in most situations. The thing that you might think about though is more your odds. Disregard your hand for a minute. Say UTG raises to 3bb. MP2, CO and the BTN call. You are currently getting 5:1 on your call. This is why it really depends on the game for me. So many people play weak-tight poker on the flop/turn that makes these 5:1 PF calls grand for the bankroll. In most of the super loose games I play in, there are really only three or four people that I don't like playing with because they will repop from the BB with air just to see it go around again. Then, they are super aggressive through the rest of the hand. In this case, I'll play a little tighter from the SB.

So, its not about "I'm half in already so I HAVE to call," but more looking at your odds, your opponents, and making profitable plays.