Alas, places that accept comments with the civility of SSI are rare. I generally pay little attention to left/right labels, but it is hard to not be at least vaguely aware of them. During the '08 financial crisis, I ran across Naked Capitalism and it became one of my go to sites to follow the action. I don't spend a lot of time there anymore, and don't read the comments, and don't comment myself, so can't speak to how you would be treated. I know they had a problem with trolls and rudeness and shut down comments for awhile but some comments seem to be back. It is heavily finance and economics, rather than purely politically oriented, but the daily links are diverse and often entertaining. And the authors on the site for the most part know their stuff. It would probably qualify as "lefty" leaning.