Do you know which exact type of brain damage he suffers from? Because it states while damage in one affected area can have an effect on your political opinion, damage in different areas show no difference whatsoever. It wouldn't surprise me to see if other types of brain damage could make you more liberal too. We do know liberal and conservative brains show some differences, so different damage in different areas could make you swing either way. I mean neuroscience is still in it's infancy, so a lot of this is just observing and trying to see patterns. Saying "brain damage makes you conservative" is too broad of a claim. It's certainly not backed by this study.
EDIT: One more thing I don't really understand is what this argument is trying to achive anyway. Do you want to take voting rights from people who had a stroke because they can't decide for themselves? This topic is really thin ice and it's usually fascist groups that propose such things.
You don‘t have to take me seriously, though I think you probably should when I warn you about the dark path you‘re walking here. It‘s enough to take the study you provided seriously which is not as conclusive as you make it to be. Certainly not enough to boil political views down to a summarized medical record.