My tools serve me, not the other way around. It’s not worth the time and effort to wash by hand or sharpen on a whetstone. I don’t need an expensive knife to cook at home. A pull through sharpener and honing steel are adequate. Get the right material and you don’t have to worry about the metal in the dishwasher.
Not seeing how a dishwasher dulls knives, unless you’re banging them around.
I’ve heard this for decades, I wash my steak knives all the time, the dishwasher doesn’t affect their sharpness at all (and they’re proper sharp knives, not those bullshit serrated things).
Water corrodes the edge. Razors stay sharp for much longer as well if you store them in mineral oil after use rather than just put it onto the shelve while still wet.
When all the utensils are in the rack, and you shove a knife in, it scratches against the other utensils, or even the plastic, and moves around depending on pressure during wash. That’s why it “can” dull your knives.
It won’t be as much of an issue with a serrated knife
Also depends on the metal alloy. Some that make great knives do not have very high corrosion resistance, and a dishwasher isn’t a nice place chemically for a reason.
Even some expensive knives can come out spotted and not great after one trip through.