There's no harm in holding them. The stress thing is only if they are very little and on the edge of death. A healthy chicken can handle the minor stress of being held by a human. Hold them if you want them to let you hold them in the future. I think being able to pick up and hold any one of your chickens is essential, because sooner or later one of them will have a problem, and you'll need to be able to pick it up, examine it and treat it, without having to chase it all around your property first and then tie it down next. And, if you want pet chickens, holding is even more necessary. My kids and I have been handling our chickens extensively since they hatched. Now they're 12 weeks old and my kids can pick them up and carry them around just fine. Most of them come up to perch on me. How comfortable they'll get ultimately depends on the breed, too. I have two breeds - Orpingtons and Barnevelders - and the Barnevelders have needed a LOT more handling to get them accustomed to it, and even now, if I skip a day or two, I can see them regress. While the Orpingtons are total puppies who will come to me and ask for attention even if I ignore them.