Why do philosophers think they know anything?

I have read many philosophers and have talked to many philosophers from Leibniz to Rand. I have yet to find a philosopher that doesn't contradict themselves. A lot of philosophy is just stating the obvious but rewording it in some new way. I am sure philosophers are very smart but do they really think their theories and hypothesis are correct? Being a philosopher is just like having an opinion on anything albeit more educated. But when is an opinion an opinion and when is it a fact? I understand philosophy was/is the foundation of many fields but I don't see the purpose anymore except to sound smart. <br><br>EDIT: Wow thanks for all the comments! Glad I could start a good discussion