Bronson should have shown restraint.
CONTAINS SPOILERS
To be fair, the bad guy did warn Bronson that he would kill the girl - but Bronson did not listen. He kept on coming at the other guy until the guy delivered his promise and killed the girl. Bronson pushed the guy into it. He did warn Bronson. Here is the unacceptable part - Bronson then mercilessly blows him to pieces.
The man was trying to reason with Bronson and gave him ample warning but Bronson just opted for a violent conclusion. Bronson should have not killed the man - especially as the guy was trying to make concessions for Brosnan.
Bronson brought it on himself.