I'll preface this with the fact that we have always had pet dogs (mutts, poodles, Shiba Inus and Aussies) --- from when I was a child to now (middle age). Love every dog of any kind, breed, size, etc... and we have 2 immensely smart, mostly well-trained dogs now (..... who should never go to WDW.) Way too much change, fireworks, sounds, stimulation, people, lights, etc.. for them to have to cope with. I guess selfishly we could want them there but dogs aren't people and these things can cause them stress...
Totally get that certified therapy dogs (they should be allowed as they are extremely well trained and will not soil a floor, a bed, a carpet, etc... and won't bark a ton......) belong at resorts and parks --- people need them to be their eyes, ears, or other sense. These dogs are usually with their owners throughout the day so they won't be left in the room alone and again both owner and dog are well trained.... I have zero issue with such dog being in a room/park/bus....
The issue comes for me with non-certified therapy dogs and private non-therapy dogs.... They are in no way trained the same way as certified dogs (also mail/email/online certification is pure bunk for dogs.... ) with regard to dealing with new people, new places, etc... I have seen some people claim the most ill-behaved and unsocialized dogs to be "therapy" dogs --- totally insane.
We love dogs but think that aside from true certified therapy dogs (seeing eye, seizure-sensing, etc...) that dogs don't belong in hotels. We pay a lot of money to ensure that our dogs are safe while we are away and that they are stimulated, and having fun and wish others would leave their pet dogs at home too.