"Try exercising your 2nd Amendment rights (buy, possess, purchase, sell-whatever) without a photo ID. "

You bring up a couple of issues here.  First, there is nothing in the constitution that states you must show a photo ID to buy a gun.  That restriction is placed on the business sale of guns to people - which also usually requires people to go through background checks and such.  However, there is no such requirement for seeing a photo ID for private sales or "gifts" of guns.  Your point also brings up another issue in that requiring a photo ID to purchase a gun, again, tends to affect the poor/minority groups much more than others....which often leads to those people obtaining guns illegally, or through other legal means (as described above).

The poor/indigent are also probably not going to check in at the doctors office very much, or are writing a lot of checks or staying in quality hotels, or even applying for jobs.  What you consider normal, many other consider a luxuary.