The rules are clear.
If these reports are tru, anyone caught thieving from their employer deserves everything that comes their way: if that includes termination, so be it. The shame should not stop there - why not charge a couple of culprits and let them have a criminal conviction. This would soon stop the theft. So as to be even handed, a search policy should also extend to pilots as well as the flight attendants.
Unfortunately a minority give the majority a bad name, and its up to the majority - including the unions - to weed out the petty criminals. However, the unions will insist on a deal being done whereby the culprits are allowed resign without character blemish with the majority of good people carrying the generalised stigma of 'thief'. Time to speak up people.
BTW, does consumption on board of unused first and business class food in lieu of or in addition to supplied crew meals equate to theft?