I really loved Frankl's book as a teenager. I only learnt about his dark side, that the book was full of lies, recently. I didn't just read the wikipedia page, followed up the references, reading into several books that go into detail about it. The more you learn, the more disturbing and weird it gets. Yes in fact they do sound like disturbing Mengele-like experiments on people. His massive-bestseller book makes it sound like he was in Auschwitz for a long period, which is a total lie. (Did you read it? I can't imagine anyone who loved the book thinking it "irrelevant" whether he actually was at Auschwitz!)

edit: Gee, you're right about the wikpedia page! The controversy section has been entirely erased since I last looked! Very weird. Sorry about that. e.g. in April last year it looked like

https://en.wikipedia.org/w/index.php?title=Viktor_Frankl&typ...

I guess all the references to things have been removed too. I'm not sure why. The books and papers it led me to seemed believable.