People tend to flock to where the group-think is. Very few people want to be challenged about what they believe on a daily basis- it takes a lot of work, especially if you're willing to admit the possibility you might be wrong. Slashdot tends to have a variety of (highly nerd-centric) views, so it's easy to find a bunch of people who passionately agree with you on issues that most people don't care about: File sharing, the best Star Trek Captain, Emacs vs. Vi, etc. There will be the heretics who disagree with you, but you can always mod up those you agree with and ignore the rest.

That being said, Slashdot would be horrible as my only news source. It's got a huge number of opinions, but most of them are the idealistic ravings of an intelligent but dysfunctional individual with minimal real-world experience. (Something like 80% of non-troll posts are in this category, including most of my own). Then you've got the corporate shills, the grammar Nazis, and the occasional individual who knows what he's talking about. Plus, there are all these rambling posts that are almost on topic, but don't really address the issue at hand- not to mention the article.