I don't think it is. There was a time in the 90s when AOL was in a similarly dominant position with much stricter moderation policies, but the marketplace of ideas never felt crippled. Everyone just understood that the AOL sandbox was a sanitized common ground, and if you wanted frank discussions on complex or controversial topics you needed to go elsewhere. (And I don't know of any topic, no matter how controversial or offensive, that doesn't have some active forum where it's regularly discussed.)