After seeing what PageRank can do in terms of controlling spam, VCs would be reluctant to fund a startup that is much more prone to spamming (e.g., something like wikipedia, social bookmarking, etc.). So one might argue that PageRank has in fact discouraged people from even thinking about social apps for a long time.
If it's on the web, spam will always be a possibility. I don't see people getting discouraged from creating networks due to spam. Any quarter-decent social application will have some measures for dealing with it.
Most social applications aren't aiming for the PageRank either. Their use is grown through word of mouth approaches, not organic search. What aspect of PageRank is doing this discouraging of social apps?
The problem is that PageRank puts you in a mindset of creating sophisticated algorithms that are much more resistant to spam than naive approaches. In that sense, it discourages people from even trying out social apps.
I don't see many people being discouraged to make social apps. A lot of the internet is based on social interaction (forums, comments, reviews, chats..) and wherever there is spam there are anti spam-measure in place that work reasonably well since these apps are all pretty usable. Maybe I just don't get what you mean
I don't think it's obvious at all that you can control spam in a social app such as wikipedia or social bookmarking. You need to try it out and see what happens.
