Man, I wouldn't, but that's me. I mean, you can't hardly kill marigolds, so I think they'll do fine whatever you decide. I think some people are pinchers and some aren't. I'm not, but maybe that's just because I wouldn't have any confidence about where to pinch each of the bajillion different varieties I grow. I dunno, maybe if you have some sort of real tall variety of marigold, all of mine are very compact and short as it is. Like they don't have really 'sets' of leaves like taller plants, they are just sort of a bit of stem, then one set of the ferny leaves.

NO, No, NO
Don't pinch back marigolds. They don't neeed it. They branch out and get bushy quite naturally. In my experience even the taller ones get bushy. That's the whole premise for pinching things back--to make them bush out.

Whenever you think about pinching anything back, ask yourself "do I need to do this to make it bushier" If the answer is yes then pinch--if it's no then leave them alone

A plant is programmed to grow and produce seeds. The leader--top--is boss and the good goes to it to produce seeds. What's left over goes to the branches. If you remove the top leaves and a bit of the stem the plant goes into survival mode and produces lots of stems so it can do what it is programmed to do and produce seeds. These stems unlike the leader are all equal and the good is divided equally to them all, so you get a bushy plant.

Sometimes when we deadhead we do this naturally. Like with Marigolds. Remove the top flower after it dies and you are pinching it back and it produces more branches and as a consequence more flowers.

Pinching ANYTHING is purely optional. It is never required. When in doubt, don't pinch and as other have said there is definitely no need to pinch marigolds.

Dave