That's my fucking point. Why do they feel the need to add drama that doesn't even make sense? There's no way that the public would undermine Saitama's achievements when he punched the rain away. They probably even felt the shockwave from his punch.
I don't think this is forced. Saitama, as this seen should be the second example so far in this series, will play the bad guy if its necessary to bring people together. If you really want to over-analyze this then the fact of the matter is that those people are all in a state of shock trying to rationalize seeing the people they call heros (folks who are he last barrier between them and extinction in their world) be destroyed. Seeing they people who are ranked to protected them get taken out and the one below them take out the monster may be easily be acceptable by you but what's a more pleasant interpretation would be those who you trusted to do the work mattered and if the weakest amongst them finished it then the power-base you've come to believe in is something you will ignore details to continue to do so. This is just human nature.
It's still my personal theory but I believe One is making Saitama a Christ-like figure. It would be a stretch to say that Saitama has a savior complex but I feel he has a very strong belief that being a hero is selfish thing even if that existence means being the most selfless being alive and this is why he's able to take in peoples hate and confusion as burdens. To Saitama, that emotional pain is the same pain as the donkey punch from the Sea King -- if he can't handle either type of pain then what does it mean to be powerful. This is the other aspect I think the author is going for -- to prove that he's become this powerful being he wished to become, he's not only willing to face the greatest physical pain by taken on the strongest but he's also willing to take on the greatest mental pain by focusing all of it on himself. It's a selfish act for him but is the perfect selfless act that's a result of home he wished to be.
It makes me excited to see whether this to its extreme will break Saitama and if my feelings bare out, the payoff will be powerful and tragically beautiful. So that's all an over-analysis while we're at it but I fall on the side of something really great is being carefully built up and not forced.