post moderation is automatically in effect for.
new users
or users from ip addresses that are known for spam attacks
auto-moderation is also switched on based on content - certain key words or urls, or image tags.
As you make more valid posts, your 'trust' level will grow and the system will stop auto-moderation.
However, if your content is not Anti-American enough (when that particular attribute is reqd) than you may run afoul of the moderators yet again. It is a balancing act members are happy to partake in -like balancing on the head of a pin ( or *****)