You expressed your opinion.
In response, I expressed my opinion,
which was different from your opinion
In response to me expressing an opinion
different from your opinion
I'M ENTITLED TO EXPRESS MY OPINION!
as though by expressing an opinion
at variance with your opinion
I had been denying your right to express your opinion
which, of course, I hadn't.
"Vaccines cause autism" is not an opinion.
It is a lie.
A dangerous lie.