Quote Originally Posted by Rater202 View Post
In the very first meeting Saitama sat in on, it was said by the old martial arts guy that he was there becuase he was only not an S-Rank on technicalities and that based on his skills he'd be there sooner rather than later.
True, but Silver Fang's opinion was in the minority- he had gauged Saitama's strength as being S-rank-level even at that point, although he still underestimated him considerably. Saitama mostly just tagged along with Genos (seemingly out of nothing more than curiousity), and nobody seemed to care that much, at least not enough to fuss at Genos about it. I suspect it's (the?) The Doctor principle- act like you belong somewhere with sufficient confidence, and often enough people will go along with it without even necessarily worrying about it that much.

And even if the 'pop up and everything in the vicinity dies' monster under discussion was highly intelligent, the odds are that it would, at most, cause a significant restructuring of human society, but nothing beyond that- certainly not an extinction event. And frankly, if it got problematic enough, odds are good that someone would just up and nuke the thing, populated area or not.