Says who? I'm all for open source (and even actively contribute), and I do not have a left-leaning political stance. Loving open source does not mean that I want to raise taxes, or that I want gendering to be a thing (theres an issue in languages that dont have a gender-neutral plural).
Why couldnt one be conservative and like free software at the same time?
(Actual queation): Why would you say its in my self-interest to vote for a left party (which would generally mean paying even more that the current 45% income taxes)?