Modern conservatism is based on fear and hatred of the ‘other.’ “Immigrants” (brown people with accents), gays, ‘wrong’ religions (mostly those practiced by brown people with accents), etc.

Your grandfather is scared of them, and hates them for making him scared. It’s rooted in racism and phobias. No justification from him will change it.

As you get older, you will have the option to agree with him, ignore his behaviour for the sake of family harmony, or aggressively reject his beliefs - which will potentially mean rejecting him. Choose wisely, and keep your compassion alive.