Recently I traveled on the Chicago and St. Louis Metro and Amtrak. And as always I was impressed by security on these systems compared to IE and LUAS
St. Louis metro has security at every station and visits on the train too. All eating drinking, loud music and foul language is banned too. Chicago with it many stations are staffed too
Amtrak has crew on intercity services. Guess what you are told in no uncertain terms that if you cause a problem you will be removed from the train, example, smoking rudeness to crew and passengers.
We have terrible problems on public transport affecting crews if they are around and passengers. The only way we will solve the problem is to educate passengers in the way they should behave when using trains and be clear about rules. Crews on trains and meaningful support for them and enforcement of those rule by a transport police.