There are clear methods to decide if a company has dominant position or not. It has nothing to do with whether you can use another one or not. Perhaps you don't have an idea what you are talking about.
You're wrong, simple as that. Being dominant simply is not enough. The FTC couldn't even make a case against Google, a far more dominant company than Facebook. You're just making shit up dude, just stop, there is no case here for anti-trust nor will there be.
You frequently break the HN guidelines by being uncivil. This is not ok, and we've warned you many times before. If you keep doing it we're going to ban you, despite the fact that we (and I personally) have bent over backwards to avoid doing that.