Shoplifting is stealing, and stealing is wrong (most of the time, anyway). However, scanning people as they leave a store is also wrong and should not be tolerated.

Interfering with these scanners is both an ethical, and productive thing to do. I applaud anyone who reduces their efficacy, even if they shoplift in the process. Sometimes, two wrongs do make a right.

Many retail stores have forgone the scanners in favour of door nazis, who will attempt to search your belongings as you leave the store, and compare them to your reciept. I urge everyone to refuse this search; remember, you have no obligation to prove your innocence. I cannot speak for US law, but here in Canada if a search is forced, and no evidence is found, you get to sue them till they bleed. (of course, IANAL).
Pakaran: Not in my country (Well, except perhaps for #3). What's illegal about carrying around one of those little stickers that triggers the sensors?