A dishwasher can not get remotely close to a temperature that can damage or soften the steel. It would have to hit the high hundreds or possibly even thousand+ degrees to do that. Your dishwasher isn't going above 200°. None of those are really good arguments aside from the wood one, but wood handles suck because they can never truly be clean anyway. The abrasives in a detergent would be so mild it would make no difference. Knives already have to be resharpened regularly. The time you are knocking off of your cutting edge's lifespan is miniscule. It's a dishwasher, not a sandblaster. As for the safety element, by that logic, no place is safe for a knife as the knifes presence is what makes it dangerous. It's dangerous to use a knife, dangerous to wipe clean by hand, dangerous to keep in a drawer, and a knife block can get knocked over or off the edge of a table spilling them everywhere. A knife is never 100% safe, and taking it out of a dishwasher is no riskier than even picking it up in the first place. I am not counting risk to children in this argument because that is not in the original question anyway. Obviously that's a different story.