If we can eat all our nutrients and still have enough calories / points / syns or whatever left over to incorporate a little indulgence into the plan - we should go ahead and enjoy them without guilt.
Amen, sister (as they say hereabouts).
I also think it's an important skill to be able to enjoy in moderation when the social situation calls for it. Gloomily eyeballing everyone else's pizza while eating a small dry salad is a pretty miserable experience - and the people around you are going to get the impression that you're no fun to be with. Tossing your plan to the wind and eating half a pizza yourself makes it harder to get back on plan the next meal. But if you can focus on contributing to the conversation (which means your mouth is mostly busy talking, not eating) so that you pace your slice or two to last as long as others are eating, you'll probably stay within your calorie targets while being fun to be around and not feeling deprived.