Is it better to identify that we have disabilities or should we be checking the block I do not wish to answer?

Identify it, as if something goes wrong, and it pertains to a disability you did not disclose, the repercussions could be quite unfavorable for you on various levels... This is one I have seen actually happen, so if you have it, then list it. You may be hurting yourself on a large scale by not doing so...

If the Answer is Yes I have PTSD some may very well not want to tell anyone about it. There is a stigma about such things. The lay person will just say he or she is Crazy or he or she is a Crazy Vet and therefore dangerous. Then there are those who hate our uniform and will use anything they can to attack those who serve or have served.
I walked in to a McDonalds in uniform and ordered breakfast one day and the young man in his late teens or early 20's glared at me, he also happened to look middle Eastern. Later on I went to the same McDonalds and he was now a manager, I was in civilian clothes but he remembered be and gave me the same I hate you with every fiber of my being look. I doubt that if a veteran tried to get job with him as the manger they would have a chance in hell. So listing your disabilities could hurt your chances of employment in some cases.

It depends. Of the disability is something you need a reasonable accommodation for it is good to be up front about it. If it is something that you do not need anything from your employer for then no need to mention it.