Like for prostitution and theft.. it's like they purposely tempt people so they can mess up their lives..
There is a line that law enforcement can not cross when using bait to catch a criminal. It is called entrapment. If you are using bait, like an undercover cop posing as a prostitute, the undercover cop can go to a place known for prostitution and stand there and wait till someone approaches her. She can not be standing out on the street waving cars down. Basically the cops can not tempt you to do something you otherwise would not have done. For example, they can't leave a bag of pot laying on the street and wait for someone to pick it up and then arrest the person for possession. But they can pretend to be a dealer and wait for someone to approach them.
True but entrapment is not an air-tight defense and the standard for what constitutes entrapment has varied over the years. Some convictions that were rather egregious examples of entrapment have been upheld by the courts. The "bag of marijuana" example would probably not be entrapment. The entrapment defense requires law enforcement to persuade someone to commit a crime; simply giving them the opportunity to commit a crime isn't sufficient. Note that a common sting operation is to leave the keys in a car rigged to trap the thieves that attempt to steal it.
They set up bait traps to, well... catch criminals.
They don't force anyone to take the bait... so they are not messing anyone's life up. The person who takes the bait CHOOSES to take the bait and mess their own life up. They have a brain, and they shouldn't do the crime if they can't do the time.
Bad choices have consequences, and if you don't think about the consequences or don't even care... then that's nobody's fault but your own.
They are rooting out the people that give into temptations and do things against the law. If there are illegal activities taking place, whoever is in charge of security is in charge of ridding anything illegal to the best of his or her ability. Their whole occupation revolves around catching and punishing people who do illegal things.
I think it would depend on what the bait trap is for me to judge it. There are some situations I can come up with where it could be useful, to catch the people already doing the crime. However, I can also think of plenty of instances where it would just be setting up a temptation for people to commit a crime and get caught.
Because criminals need to be caught. Bait traps are sometimes the best way to catch them. They can't break the law and get away with it, they need to pay the consequences for their actions. Prostitutes and thieves can't get off 'scot-free'. That's why we have cops; to make sure laws are being followed.
You are right, my bag of marijuana scenario is not accurate. A cop asking someone to take some marijuana for free might be though. I do realize that entrapment is rarely a successful defense.
Preventative measures. I'd much rather they set the traps than give the criminals the opportunity to go for the real thing. Example: child molesters