If it is that nebulous and fluid how do you know that you are a pagan if there are no clear guidelines on what a pagan is?
It is actually quite simple.
You look at the world and its religions, starting, in all probability, with that of your parents, and sometimes you get to point where you start to question that religion, its beliefs, its rules, its rituals (all church services are forms of ritual), and its attitudes to people, to other religions, to nature, to everything that it stands for.
Sometimes you find that there is nothing in the religion with which you fundamentally disagree - brilliant, happy, happy, days, carry on regardless.
If there is something that you find yourself at odds with, for instance - why are all the people running the ritual, the clergy, male and why are the wearing dresses?
Presumably the first people you will address this question to is your parents - if their answer satisfies you, move on to the next question. If all your questions are satisfactorily answered - again, happy days.
If not you move on to the Clergy and the library and try to find answers there.
If you do not find the answers you start looking at religions other than that in which you were raised. Some find what they want in the organised religions, others do not; of these last some will become atheist or anti-theist, some will investigate the non-organised religions - most of which are deemed pagan by the organised religions.
Paganism is the home of those who reject the philosophies of organised religion but equally reject the dogma of atheism. This is why modern paganism, neo-paganism is such a personal belief/religion. Some pagans do not call paganism a religion at all, mainly because of the connotation with all that they have rejected.
Yes, we are seen as the clowns of the religious world; fine, so be it, if you don’t like it reject it and us, but don't take the piss as, during our journey to paganism, we have, most of us, learned how to take the piss back and believe me the adherents of the organised religions and atheism do not like that and will always deny that they have ever taken the piss at all!
You don't believe me? Read these pages, but do it with an open mind.