I'm just curious ... so a hypothetical for your consideration:

If I were to run a website in which people could submit writing and even comment directly, as well as provide relevant links and resources, and declared what could be construed as a sociopolitical or spiritual message intended to be spread among the masses, what reason would I have to prevent people from viewing the material unless they first registered a membership?

If I was trying to get someone elected to office, why would I want to make people join the campaign before giving them the information that might compel them to do so anyway?

If I'm spreading a religious salvation message for all humankind, why would I want to keep people away from my gospels?

Let us be clear: there would be no fees charged of users. Free membership, just like we have here. Unlike our arrangement here, though, guests would not be allowed to read the contents of the website.

The only reason I can think of is bandwidth control.

But I'm not that much of a tech-head, so I figure there's obviously something I'm missing.

Furthermore, let us presume that, claiming integrity according to the agenda, I should not be selling or distributing that information to advertisers or spammers.

So what am I missing? A guy goes to Google, looking for a resource, sees my link near the top of the list, reads the blurb, clicks the link, and bang! the article isn't there for him unless he registers a membership.

Is there a practical reason to do so?

Maybe it's a wishful way of counting followers. :p

I think it is all about advertising. And maybe harvesting email addresses for future spamming, at least in some cases. But I imagine it is similar to magazine subscriptions. When we were recruited to hawk magazines door to door in junior high, the guy told us that magazines make their money from advertisers, and they attract advertisers by having a large subscription base to prove that people would see the ad. I imagine that online newspapers and magazines now work that way. Speculation on my part, I have no factual insight into the business model used by online newspapers.

Considering the type of websites you mention, and assuming as you did that they are not selling their users' information, there is no technical reason aside from bandwidth to restrict the viewing of their content to registered members. The only practical reason I could think of would be to prevent a huge influx of random internet users, e.g. a site being "Slashdotted." Aside from that I would venture that there is absolutely no benefit whatsoever to excluding the anonymous internet user.

But as far as the political and religious type of sites, there is the possibility that they know that their message is flawed or otherwise "sketchy" and therefore want to attempt to ensure a commitment to them before allowing any access to the content. (A semi-comparable real-world example being US President Bush's requirement that all people attending his 2004 campaign stops be required to sign an oath that they support Bush -- no dissenting opinions allowed.)

For other websites outside those you referred to, there could be a variety of reasons to require a free membership to view their content. Some could possibly be selling user information, but that is unlikely for the majority of (legitimate) websites. More likely, they have content that they consider valuable enough or bandwidth intensive enough to at least require knowing who is accessing it and having more control over bandwidth. e.g. - If a site was offering downloads they might want to ensure that users can only download it once. Or, if a site had many images available for view, they may want to prevent a huge influx of random internet users (I can think of a few online forums which allow you to freely view their content but if a post contains an image or link to an image which is hosted by the site you must register to view that.)

And of course requiring a paid membership has it's own set of reasons. But I already answered far more than you asked and probably more than you cared to read. :p