I tend to limit my use of "science denier" when an organization or its followers systematically deny scientific knowledge on multiple unrelated fronts.
Interestingly, I have read that in the 1920s and 30s, there was actually an organized relativity denialist movement, that wrote articles and held public protests.
Relativity was a huge philosophical shift from the comparative simplicity of Newton's laws. It's not surprising that there was resistance to it.
Tesla was famously against relativity, telling the New York Times, "Einstein’s relativity work is a magnificent mathematical garb which fascinates, dazzles and makes people blind to the underlying errors. The theory is like a beggar clothed in purple whom ignorant people take for a king".
Indeed, and the anti-relativity movement also had a very strong undercurrent of antisemitism.
Chances are, most of the people marching against relativity had no clue about Newtonian mechanics, and were told stuff such as relativity leading to moral relativism.
Interestingly, I have read that in the 1920s and 30s, there was actually an organized relativity denialist movement, that wrote articles and held public protests.