The free groups (free.*) are similar to the alt.* groups. Every user is free to do whatever they like and that’s why most ISP’s treat free.* groups like alt.* groups. Only certain free.* groups are carried and they have to be requested by one of their customers for them to show up on the servers. Free.* groups can be created very easily because there are no rules.
The difference between free.* and alt.* is that the name free.* comes from the word freedom and most important in the free.* hierarchy is the users’ freedom of speech. Because there are no rules in alt.*, ISPs often apply filters to alt.* as a whole. Many try to filter spam, trolls or other behavior they see as abusive. While this looks like censorship to you, nobody forces you to use a certain ISP and if you are not happy with the way they filter newsgroups, you are free to go somewhere else. The free.* groups aren’t like this as no rules apply to them.
If an ISP filters in free.*, the supporters of this hierarchy will immediately complain about that, as it destroys the whole idea behind the free.* hierarchy. With this hierarchy, the idea is “no control at all,” not even if it looks like somebody is committing a net-abuse. Users shall protect themselves of abuse on their own (using filters in their news client for example).
The free hierarchy is younger than the alt hierarchy and nobody knows how it may develop in the future. It was started as an experiment some years ago and survived up to now, similar to alt.*. Nobody ever thought that alt.* will become as popular as it is today, so who knows. There are a lot of garbage groups in this hierarchy, but that is what makes it fun and exciting.