I've read the threads over at reddit where there's this popular comment that is polarizing towards this issue and that why should there be saving if this guy basically just killed off an entire city.
And well, despite being annoyed by the tropes this series have had at times, this chapter was pretty good.
I think in some way, Deku have surpassed All Might. This scene really didn't felt cheap or unearned because Shiragaki did put Deku through a lot of pain.
I mean granted he didn't murder his potential love interest/ a female character in front of him like Pain in Naruto but somehow it still felt like Deku went through enough to be justified to just say fuck it but didn't and that's inspirational.
I still don't particularly enjoy Deku as much as I did in the beginning of the series but this chapter did throwback the good old times.
People who go "lol this guy just murder so many people and saving him is stupid" have no idea how society should and is fundamentally working.
Edit: I think I understand why this is so refreshing. In Naruto, by the end of Pain arc, Naruto has been preaching about saving Sasuke for three arcs straight.
And Fairy tail is, uh fairy tail.
Yet in BnHa, none of the heroes actually thought from Shiragaki's POV or step into his shoes. The closest we had was Hawks and even then he was willing to resort to extremities and was conditioned to do so. All Might was a great figure but it was also because he exists that the League exist which in turn meant that maybe he just wasn't that good at saving people from their inner demons but was better at smashing.
So I could see how Deku's answer made an impact.