Your feelings are normal... I've been through pdd in the past, and even back then I was as totally disease paranoid as I am now :52: and believe it or not it STILL it came into my house!!!
Just as with people, diseases don't discriminate! Both the beautiful pampered beloved pet, as well as the dirty hoarder's bird are both equal in terms of exposure to these evil diseases. These viruses can be found ANYWHERE.
It will unfortunately stay in our bird community and is spread because while MOST people are well meaning, loving, responsible people who are NOT stupid, but just simply don't realize how common and in some cases highly contagious the avian viruses are, and to beware. Even worse are the people out there who not only are ignorant to diseases, but are just out to make a buck and don't care.
Sometimes no matter how careful you are, you can have bad luck. I got my beautiful (on the outside) pdd bird from what I thought was a good, clean and knowledgable bird store!! I was aware and paranoid even then, and I couldn't avoid it. I got her every other test, but that one was not available then (or very accurate).
So remember... Sometimes crap just happens. Some things are just part of our life path for some reason and we can't avoid it. Just like some really fit healthy people get cancer, and we can't understand why.