Likely because of your tone and the way you conveyed your point, rather than the point yourself. That attracts down votes as well. If your message was that this happens regardless of party, you can say just that. FWIW, I think the tone of your parent could be better as well, which may have contributed to the manner in which you posted.
Given no one has commented on why they down voted, this is just speculation on my part based on what I've seen elsewhere on HN.