As someone who lost family to the Third Reich and who hates Nazism, I don't think there's anything bad in owning WW2 era German militaria, or restoring a German plane, or doing German models or reenacting. Hell, I have built a couple Messerschmitts myself, and would love to take part in the restoration of a Stuka or Heinkel 111 bomber if one was to be dug up from an Eastern European marsh.
I think that the reprehensible thing is "Nazi memorabilia" itself: not the planes, the steel helmets or the rifles, but things directly linked to the Nazi state, system and ideology. A black SS uniform, for example, or the diaries of a death camp guard, or something belonging to a NSDAP member. I know that some people will contest that, but I think that Waffen-SS stuff should be given to museums but not used for profit as well, since they were the armed branch of the Nazi party. Wehrmacht, Luftwaffe etc stuff isn't problematic.
But what bothers me is that said politically related Nazi memorabilia IS what sells for the highest prices. If we are to believe
this article, Hitler's writing desk was sold for $422000. Four hundred and twenty-two thousand dollars. That kind of money will buy you a
bona fide villa in Torrevieja, Costa Blanca, Spain. Or an actual, flying condition
MiG-21 with import, registration, training and fuel costs covered... That thing should be in a museum, not sold for profit.