Before you press the call button, there is a potential conflict between the offending pax and the crew.
As soon as you "shop" them (notwithstanding their actions being wrong), you create a conflict between them and you.
You are now part of the problem system.
Much better to get out of the way and leave the fallout to the crew to deal with.
Much better than that for the crew to maintain situational awareness of what's happening in the cabin and sort it out, rather than saying something and not following through.