> A political essay is (typically) written by certain persons to
> persuade the public of a certain position. If it is modified,
> it does not do its job. So it makes sense, socially, to say
> that these cannot be modified.
Then, why are there so many political essays under the GFDL,
without invariant sections?
You'd have to ask their authors about that. I won't criticize their
decisions, but I don't see a reason to do it.