Very directly, I would say, by making the barrier to running your own low-traffic website too high. Modern social media is all about hosting content - microblogs, photos, etc. Geocities was an early workaround to an inability to host things, and it's worth remembering that MySpace was originally positioned as a kind of evolution of that with the social aspects bolted on - it (notoriously) allowed arbitrary HTML, so that you could make your own "homepage" on the internet. Facebook further evolved this, offering a much more restricted experience. Were it not for NAT, I would have expected an explosion in tiny self-hosted personal sites around the time that dialup was replaced by always-on cable connections, and before long we would probably have had various wordpress-like frameworks to do the social aspects. Which is not to say we wouldn't have eventually had a Facebook-like entity, but it would have faced much stiffer competition than it did, and people would perhaps have been less forgiving of its restrictions if they'd had an easily-accessible wild-west to compare it to.