Platforms that support downvotes (including HN) are prone to groupthink and vote bullying. Going against the popular view--either site-wide or against the popular view of the people who access a given comment thread--will result in downvotes even when posting material that's factually accurate. This tends to create a self-amplifying process where established views become more entrenched and, possibly, more extreme.
For example, the majority view among people who access COVID-19 posts on HN is that the disease is not a major risk. Anything posted to the contrary is highly likely to be be downvoted and/or flagged for removal. This drives away factual information in favor of groupthink and creates nothing more than a single-sided echo chamber.
HN is no better than Reddit in this regard; it's just that the groupthink hot buttons on HN are different from those on Reddit.
As this view itself is a view that runs against the universally accepted wisdom on HN, this post itself has already been downvoted and will likely be downvoted further.
As a matter of personal ethics, I only downvote material that is socially hazardous (e.g. COVID-19 misinformation), seemingly inorganic, or seemingly dishonest. Being wrong in good faith isn't a karma crime and shouldn't be punished. Unfortunately this is far from a universally accepted perspective.
With regard to why both-sides-bad arguments are not well received in the context of US politics, I feel newen covered most of that in his/her reply to you. However, I will add that 'both-sides-bad' has a really long history of being used disingenuously by the right wing, both directly and by paying left wing fringe candidates who use 'both-sides-bad' messaging to split the Democratic vote.
Both sides are indeed bad (see: e.g. Obama's execution-by-drone policy), but one side is far worse than the other (see: e.g. Trump's children-in-cages policy) and 'both-sides-bad' is usually used by the right wing as a way to trivialize Republican abuses. People who pay attention to US politics tend to be aware of this and will be less inclined to give 'both-sides-bad' comments the benefit of the doubt.
Further, on the question of respect for democratic rights, the factual history of voter suppression in the United States is so black-and-white (literally: it's a history of white conservatives preventing black people from voting) that anyone who does a 'both-sides-bad' take on this is either grossly uninformed or dishonest. Neither option will be well received by people who pay attention to these kind of issues.