Yes, fundamentalism and extremism comes in many colors, both theist and atheist. As does moderation.
My point exactly. But at least theist belief systems have
something in common - indeed a ‘something’ that is generally central to the system - whereas atheist belief systems only have a
nothing - the absence of something - in common.
Granted my example was poorly chosen, overly coloured by the other post I was responding to, but take instead the example of Catholicism and Hinduism, shamanism, spiritualism, satanism and neopaganism. All very different, but they have at least the common belief in a God.
Despite this it would be nonsensical to claim that ‘theism’ was
a belief system. That is like saying that a spark plug is an engine. Theism, or spark plugs, are merely
components in belief systems or engines.
It would be even more nonsensical to say that
the absence of spark plugs is ‘an engine’ - at least two engines which both have spark plugs have
something in common. Both are almost certainly internal combustion engines, for example. Whereas two ‘engines’ that
lack spark plugs need have nothing in common. They might be diesel engines, steam engines, Stirling engines, electrical motors, clockwork or (stretching the definition a little) a horse.
Likewise, it is more sensible to compare Catholicism and Satanism, which at least share a lot of beliefs, than to compare western atheism and Maoism, which really share only the lack of a belief.