The scientific consensus
Oh so Galileo was wrong? I mean, consensus and all that.
Galileo was right about many things, and he was wrong about a few as well. Likewise, the current scientific consensus has been wrong about things in the past. Science isn't perfect.
But historically, the scientific mainstream has always been correct *vastly* more often than fringe scientists who claim that it's all a hoax. Of course, each time, the fringe scientists will say "Well, mainstream science has been right *before* but this time it's different." That's been true in every decade, whether it's the 1890s or the 1960s or now.
Back in the 1960s, the leftists hippies were all about saying how science was just a tool for "The Man" to fool the populace. And in a handful of cases, maybe they were right. But overall, they were hugely wrong.
Specifically for the case of covid-19, it's something where governments and scientists of vastly different countries all agree on most points - from Israel to Germany to Brazil to South Korea to the U.S. Imagining that all of those governments would cooperate together on a hoax seems quite a stretch.