This is a perfect example of how the news media takes a sound bite of an innocent off-the-cuff remark and twists it to denigrate Trump. Looking at the entire context, Trump in no way was marginalizing the value of a purple heart as he was totally honored by the gift and was respectful as well as genuinely thankful to the veteran who chose to give it to him.
If Trump had half a clue for being respectful of the military, its traditions, and the sacrifices necessary to be awarded a Purple Heart, he'd not "accept" it....."I always wanted one. Gee, thanks!"...but would have, instead, pinned on the chest of the vet offering it, thanked said vet for his service and sacrifice, and had most everyone cheering, both in the audience and those watching later.
Instead, he took it and dishonored/discredited the meaning behind the medal. The vet was wrong in my opinion even offering it to Trump.