IMO, the controversy comes down two issues: Are the gains permanent? and there is bad press caused by pics everywhere of extremists with weird-looking cocks.
I can’t say whether the gains are “permanent” or not. All I can tell you is that I got an inch of length and some added girth from pumping alone with no other PE exercise. It didn’t go away. Maybe, had I stopped all pumping, it would have gone away. But maybe, too, if I stopped all PE completely, I’d lose some of the pumping gain and some of the gain I’ve got since adding other exercises.
On the other hand, I’ve read posts here and at PE Forums from guys who quit everything for a year or more and say they kept their gains. There are no formal studies to rely on for answers.
The pics you can see in nearly all the pumping galleries celebrate certain tissue distortions which occur as a result of over-pumping. The owners of these cocks are happy with their results, some of which look sexually unappealing and non-functional to many who are considering pumping. I held off buying a pump for a year because I was afraid I’d get that. The impression left to most uninformed viewers is that this is what pumping will give you and that pumping is dangerous.
The fact is that sensible pumpers do not get these distortions, they just end up longer and thicker and often with improved erectile function. But we don’t see as many healthy-looking cocks in these galleries as we do warped ones, hence the bad press pumping still receives.