90% of these people are just poor peons looking for a better life. Half the time they're chasing them, they're also trying to stop them from risking their lives in dangerous gambles to cross the border. With all the commercial traffic between the US and Mexico, smuggling is generally passive in that it's hidden in cargo, etc. Most of the Customs stuff is the same.
Smugglers and other criminals are serious desperados though to be sure. The Border Patrol has a colorful history in shooting it out with real banditos. So it's not a safe profession.
BP agents are some of the best trackers in the world though believe it or not. They can usually tell right away if it's a bunch of families, or a couple of smugglers. If they run across a mixed group of them, then they will also try to protect the illegals from the criminals even if they're all trying to cross the border in the same mob. That means sorting out illegals (similar to refugees in level of threat) from bad guys right on the spot, usually at night, alone or with little back-up.
I doubt that there's too many Law Enforcment officers that take pot shots at men, women, and children who are just crossing the second easiest border in the world to transit.
Ross