Some clarity for folks who don't get it:
- Rudeus's face when slavery is brought up? Not so much as an eye twitch. Seems that prior to this chapter he had already accepted slavery to be as mundane as the air he breathes.
-At no point was Rudeus's thought process anything remotely close to "I want to save someone".
-He was about to kill her. No seriously, did it look like he was joking? If she said she wanted to die what do you think he would've done, walk off?
The point of this chapter wasn't heroics, it was empathy. People are getting empathy confused with sympathy here. He had no sympathy for her "suffering" as a slave, hell we don't even know why she was sold nor does that matter since it wasn't the point of his exchange with her in this chapter.
Rudeus empathized with the lack of hope in her eyes. I felt like that was very well done (I admit I popped off a bit, that was hype). If his life were to turn around a bit more then perhaps he'd find it in his heart to become the hero for someone else that Roxy was to him, and we could see a spark of hope for that in this chapter. Unfortunately it seems to only be a passing thought, though I feel like it is very human of him not to have progressed far enough in character development to be a less self-serving person yet.
Anything else you read in this comment section is probably just projection. Buying a slave isn't saving slaves, ending slavery is saving slaves. Rudeus has no intention of doing the latter, he's not being "portrayed by the manga as a hero" like some people think he is, and there is nothing cliche about slavery existing in a fantasy manga when the real thing was legal only 150 years ago IRL (and is still happening illegally in the form of trafficking tbh).