It's not "public opinion" — you would expect most quote tweeters to be people who follow this person (or follow other quote tweeters), i.e. people who generally agree with him already. This is a great example of selection bias.
Are most quote tweets not dunks on the original tweeter?
I don't know about "most". But either way, the operating mechanism is that some person has amplified the quoted tweet to an audience that already agrees with them. The dunk tweet scenario is also an example of selection bias.
If it gets popular enough outside of twitter, maybe. But with the spread limited to the quote tweets themselves, only followers will see it initially and those followers are much less likely to have a large follower-base of their own to spread it.