The implication of your GP that your parent is implicitly criticizing is that merely having a political affiliation disqualifies one's opinions by default on matters of opposing political matters. I'd agree that was the implication made by the GP, and I'd agree that it's a destructive oversimplification.
If you're going to make claims like this then you need to provide evidence.
Because all I can see from the article is mostly a regurgitation of what was in the letter.