Stupidity: Felix and the DEA capture Sanchez, a very powerful drug lord, in a very public way, have the wedding...then everyone just goes home. No concept of extra security or concern about his minions getting revenge. So of course they can then just wander into his house with no problems whatsoever to capture him and murder his wife. Bond's clearly concerned when he learns Sanchez has escaped, but he must have realised there'd be plenty of goons still around before that point.
Stupidity: At the start of the tanker chase Sanchez shoots at Bond. He manages to get in the cab and throw the driver out, who lands on Sanchez's car. Sanchez then gets in front of Bond and has the ideal opportunity to just shoot the cab up with his machine gun knowing Bond is driving, but he doesn't.
Stupidity: The "$32 million" facility for processing the gas/cocaine apparently doesn't have a sprinkler system or any real fire control. The second the fire starts, which is still fairly small, in a single room, and could easily be contained, basically everyone evacuates the entire complex and just leaves it to burn/explode.
