The vast majority of our trips have been in August because of school/work schedules and deals.
I think you have received excellent responses of how brutal it will be.
I agree with the others, it is like the surface of the sun. We used to have a joke that when we exited our hotel, we would be internally screaming "Go back in!"
We always did EE and came back to the resort for a midday break, including swimming, showering, and napping, then went back out. The heat just zaps your energy. And your patience. And your appetite. Just everything. We still talk about one night in HS, watching Fantasmic when we were all just dying of heat. We were sitting, drinking frozen drinks, and sweat was literally dripping down our faces, backs, and everywhere else.
Yes, we did
cooling towels, misting fans, frozen water bottles, hats, umbrellas, sunblock, etc. We watched all of the shows to sit in AC, did table-service meals in AC, visited resorts for the AC, etc. When the kids were little, they would love it when the busses would arrive with condensation on the windows from the AC. They called them "refrigerator busses".
I will say the rain storms in the afternoons help with crowds. Be sure to bring more than one pair of sneakers. Nothing dries when you leave it on the balcony in that humidity.
I have detailed notebooks where I told myself never, ever again - but it was the only time we could go then.
Last year, we went to DLR for the first time - late June/early July. It was life-changing different. Cali weather is perfection. I would choose to go to DLR every time, but the (now adult) kids prefer WDW, because there are 4 parks.
This year, we are going to WDW in April for Spring Break. We know we will fight crowds, but we like crowds better than the humidity of August.
As others have said, if you can't go any other time, then go. Planning for the heat and setting appropriate expectations is key.