I would never install Facebook on my watch. Period.
That said, I also love to have the opportunity to delete any apps I want (well, maybe not a watch app) be it Apple own or 3rd party. Think about it. If you have as small a collection of apps as possible, not only your watch will run great but you can memorize the movement of the Crown and control your watch instinctively. This will be like a dream gadget for people with accessibility problems.