I totally disagree. It all depends on where your humidity is. Opening the bator can be safely done during hatch will no ill effects if you have your humidity in a safe zone. and you make sure it recovers quickly after opening it. Of course if you are opening at hatch when it's only 60% you have a greater CHANCE of causing problems. Many of us are very hands on during hatch with no ill effects. I am a meddler and constantly in my bator to remove chicks, shells, and if I have a malepositioned chick and feel it needs attention, I do that too not to mention the fact that I keep all pippers pointed up. BUT, I keep my humidity up, I keep a close eye on it while I'm fussing and I make sure that it recovers quickly after.
I do agree that often times we are the problem with low hatch rates. Many of those are not having a checked instrament and trusting something that is reading wrong and not having the proper humidity during incubation. Another big problem is hatchers assisting too soon, or when it is not even necessary.
Everyone has different methods and as long as they are working no one should critize them. Hands off people are more comfortable being hands off, that's great. Some of us are comfortable (with the same resuts) being hands on. And that's great too.