While I agree that free food is just that, I DO think common sense has to play a part. For some people, it comes naturally to just put a sensible amount on their plate or to have the control to know when they are full.
For others, including me, common sense is missing so I'll pile me plate, unconsiously eat every mouthful, feel ill and feel too bloated to do any exercise. I HAVE to make a conscious effort, which is a struggle, to watch the amount I put on my plate.
I know in probably 90% of cases free food is 100% exactly that, but some people DO need to think about portion control.