Like LaQueen, we worked hard to teach our children the appropriate behaviour for restaurants. We have had compliments on how nicely they behave, and we have had waiters and restaurant managers express pleasure at seeing us come back to their establishment. And now ds1 is away at u over situ, and ds2 is off in the autumn to start his degree, and I am confident that they have the necessary social skills to cope with whatever comes their way.
MsBella - I am afraid that you are not doing the right thing for your child by teaching him that it is OK to wander around in restaurants - he needs to learn the appropriate behaviour for them - and at the moment, you are teaching him that it is OK to wander around and interrupt other diners, and the longer you go on letting him do this, the longer you go on reinforcing the message that his behaviour is OK, and the harder it will be to teach him that actually he can't wander round under the wait staff's feet, interrupting people.
And unless he is always within your arm's reach, he IS at risk of a waiter tripping over him and injuring either him, themselves or another diner - and that would be your responsibility. If a parent is letting their child wander round a restaurant, and they trip up a waiter, causing someone else to be hurt, they could try to sue you for damages, for that injury/loss of earnings/pain and distress.
What if your child trips a waiter carrying boiling coffee, and it is tipped all over another child or a baby - would you think then that perhaps you should have made your son stay at your table?
You are going to say that those are very extreme situations, and they couldn't happen - but unless you have a crystal ball, you cannot know that. You have simply been lucky so far, that's all.