Illogical. A person's thought processes are generally more complex than that. Besides, this does not account for people who change sides based on which side they think is the most convincing at the time, all sorts of other inbetween states.

Sexuality is an example of genetics hard coding. Political affiliation, a purely ideological concept, is not. At least, there needs to be far more concrete evidence than this.

Edit

Essentially: A mix of nature and nurture is the most logical conclusion. The only question is, to what extent.