Hey /u/grizzlyandwolfk9s & /u/Brikachu, if you care about teaching people here, is some friendly advice

I totally understand the purpose of service dogs and never pet them or ask. I also have to get large groups of people on board to do things they don't want too(the reason why I am telling you this in the next paragraph).

You don't need to be condescending or a rude when you deliver this message, it is not an effective means of transferring information. A friendly explanation of the reasons why will be MUCH more effective than:

You are not entitled to pet anyone's medical equipment, period and should not be asking.

Another trainer here: you should assume the dog always needs to be focused, because there's a chance they do. Don't ask. If you see a service dog in public, there's a 100% chance they're on duty and cannot be pet.

Trainer here; we do mind, very deeply, and will only ever approve under very certain circumstances. Allowing petting conditions the dog to lose focus.

You could have said something like:

I totally understand why people would want to pet service dogs, they all seem so well trained and are generally pretty cute. Unfortunately, this ends up being really dangerous as it can distract from the service jobs task. Say the service dogs job is to monitor for a seizure, if they are distracted getting a pet they may miss the signs of a seizure. Unfortunately, even asking can be a distraction, so your best bet is to admire the dog from a distance and appreciate they are being a good dog doing a noble job.