Against specific vaccines opposition to which has been leading to measles outbreaks. I think counting that against him is important, and again it's usually what people have meant when they've said "antivax" before COVID.

He believes the net harm from the MMR vaccines is greater than the net harm from measles, and has provided the data to back this up.

And that belief is a concern if he is wrong. AFAIK, he is wrong, so I am concerned. AFAICT his "data" is the same fabricated "MMR causes autism" data as the other anti-vaxers. If you know of something he's been pushing that's not downstream of Wakefield (or even evidence of his meaningfully revising his opinion around the Lancet's retraction) I'll give it consideration, but there's a limit to how many times I'm interested in relitigating the same questions without meaningful new data.