I gotta say, regarding last episode, I'm still not ok with how slavery is handled in MT. I know the light novel explores the subject better than the anime did, but still. For Rudeus to actually buy a slave, when he initially grew up in a society where there is no slavery, and when keeping in mind that probably many of those orphans were orphaned during the Fitoa Incident, it leaves a very sour taste in my mouth.
My brother in Christ, Rudy literally kidnapped, bound and SA'd two little girls in this episode. Not once in the entire narrative has he ever been shown as an unambiguously good character, he has always shown varying (but non-zero) levels of degeneracy. It's just how his character has been written, he is not your conventional white knight hero.
To add to that: he's actually less shitty as a person in the new world than he was in Earth. And he doesn't even show the remorse that he was supposed to - he's still pissy at his old life's brothers for breaking his computer with a bat!
I hope you too will be able to see a stark difference between being a degenerate and being cool with enslaved children. I am not asking for Rudeus to kick down the door to the slavers market and declare that slavery is no more, but I do expect more than just an internal monologue to hand-wave away any moral conundrum.
Maybe you should take a better look at dictionary definitions of degenerate. There is likely only a stark difference in your own mind because of the term being normalised in your experience.
Just like Rudy has likely grown up with slaves in existence in this world. Which is bound to have normalised that for him.
Just remember how long he's lived in this world now. And use that to put things in perspective