But now we're seeing science denialism on a whole other scale. Over a thousand "scientists" signed a document that says protests for their preferred causes aren't risky, but protests against their policies are.

Why should anyone be criticised for denying this so-called "science" when the people who made it are now openly denying it as well?

Also, whilst mass gatherings themselves can act as a vector for disease transmission regardless of what the cause is and despite some forms of masks, the objection to the lockdown protests wasn't that participants might put themselves and their immediate families at risk so much as their stated goal was to end the lockdown, and thus see millions of people not involved in the protest expected to go back to work and encouraged to socialise.