Note: I'm going to try my best to avoid being snarky in this entry, but I'm writing about a pet peeve of mine-- so I promise you nothing.
You're having a problem-- maybe it's a computer problem, or maybe it's a web page problem, or a problem with some consumer electronics item. Chances are, you pull up Google and perform a quick search on your problem. The first item in the search results looks very promising. Here's another person who's experiencing the same problem you have and they've taken the time to write the problem up on a web site forum. If you're really lucky, someone out there with more expertise than you has come up with a solution and shared it on the WWW.
You click on the link, and read the first entry in the thread. Sure enough, the person is experiencing the identical issue you are! As you scroll down to read the responses, you find that all of the responses are deliberately obscured and that in order to just read them, you *must* join their website first. I don't know about you, but that sort of behavior alienates me almost instantly.
Joining the website is always "free." All I have to do is provide a working email address. No reason for me to be concerned about that, right? After all, I'm sure the people who run this website won't spam my Inbox and/or sell my email address to a third party that would do that. Just because they resort to tactics like posting just enough content to get high rankings in Google, and then deliberately withhold the resolutions to problems to force people to join, there's no reason to think they might toe the line of ethical behavior in other areas.
So much for not being snarky. ;)
I'm going to let you in on one of the secrets that builds positive web site communities. If your content isn't of a proprietary or controversial nature, do NOT force people to jump through hoops to consume it. Let people see the quality of your content; if it's useful to them, they will bookmark your site and return to it in the future. Sooner or later, they will see a thread to which they feel they can make a positive contribution-- that's when you require them to sign up. After all, we want to give people credit for positive contributions, and keep trolls from diminishing the quality of our content by making people accountable for what they post with their account. It's a lot harder to find cynical motives in that scenario.