Take a gamble on the value of the content on your web site. If it's actually valuable, your visitors will reward you by coming back, sharing and even registering. Another good point is that the people who register afterwards are a better match to what you provide (pre-qualified).
FutureLab Marketing & Strategy Innovation blog: Collecting Visitor Info: Reward vs. Reciprocity, 2009-Aug-29, by Roger Dooley:
In fact, most users confronted with a form won’t complete it....a reciprocity strategy works better – give them the info they want, and then ask for their information. In the impressively titled Embedded Persuasive Strategies to Obtain Visitors’ Data, Gamberini et al found that twice as many visitors gave up their information if they were able to access the information first.