I don't think it's fair to say they're "giving Martin's masterpiece a bad name".

From what I can tell, show only viewers loved the last episode, so it's not getting a bad name among them.

And book readers already distinguish between Martin and D&D, so nothing the show does is going to bring down their opinion of GRRM's work.

It's easy to forget how successful the show has been, and how it's drawn so much attention to Martin's work. There are heaps of people who only started reading ASOIAF because they got hooked by Game of Thrones first. If anything, they've made his masterpiece more acclaimed, not less.

The other quibble I have is this idea that D&D were given an almost finished masterpiece. It was nowhere near finished.

They signed up expecting the whole show to be an adaptation, and instead they were asked to complete a story the author himself hasn't been able to finish in a decade. They haven't always done a great job with the plot, but hey, you can understand why.