I think if someone wants to use that excuse, they should produce a substantially different adaptation of the source material, like some of the crazier variations of Shakespeare.

LOTR was mostly well done (yes please, cut Tom Bombadil and that whole pointless detour), but they also made changes for no apparent reason.

The Harry Potter movies were perhaps the worst offender, substituting perfectly decent dialogue from the books with cringeworthy kids movie crap. Just because you can, doesn't mean you should.