"By posting this, you agree to our terms and conditions"

Is it okay to have a "By posting this, you agree to our terms and conditions" (i.e. like 4chan) as opposed to a "I agree to the terms and conditions" checkbox?

I read about automatic agreement to terms of service here on UX and how autochecking these checkboxes makes them void in court. On the other hand, requiring users to check them off every time they want to post has to be bad UX, not to mention cluttering the interface.