These days they justify it by saying it's not a rip off or plagiarism, because it's an homage.
No, that's just overt cynicism. One can be inspired or influenced by someone else's work without copying it line-for-line or word-for-word. Many people can come to the same idea independently without any knowledge of what someone else is doing, and just because someone can later say the first one to the solution was ripped off by all others doesn't automatically make it true.
Was GR and other Trek creators influenced and inspired by Forbidden Planet
and other works? Yes, most likely. Did they blatantly rip off those previous works down to the last detail? No.
Hell, the essential concept for Forbidden Planet
isn't new if you look back into the SF pulps. So who was FP ripping off?