Is it appropriate or acceptable to thank a professor for their dissenting public opinion? This is a question mainly in case I haven't foreseen any potential repercussions.
The pandemic is a contentious issue, and a particular academic in my country has been outspoken with the same view as me. I'm currently a PhD student, and would just like to send an e-mail in support to said academic, especially considering that I imagine they would be the victim of many negative and/or abusive communications, again given the contentious nature of the topic.
Their field is also an application of mine, so I would be interested in discussing some of their research in that vein.
Yes.  Telling someone you appreciate their taking a public stand you agree with, thanking them for it, is always appropriate and appreciated, especially when you suspect they've taken some heat for doing so.