They would pick c. All the legislators have to do is set a minimum size and certain exceptions on what can be removed, eg above 100 million users and remove off-topic and spam. HN and 99% of websites would be unaffected, but Twitter, Facebook et al would have to be more hands off in moderation.

If you own a giant piece of land and the government wants to build a highway over a part of it, it's still possible for them to legally do it, even if you refused.