The original and fundamental philosophy of UML is to be unambiguous and understandable by most, without requiring an in-depth knowledge of a complex semantic.
This philosophy had for objective to facilitate the communication in between the different stakeholders of Software Engineering projects and to federate the notations to promote common understanding and shared vision.
It is obvious to me that the original philosophy is getting diluted progressively amongst the different additions that have been made to the standard over the years.
I do find myself very much in tune with this presentation umlbooch.ppt made by Grady Booch, and which promotes the need to address the increasing complexity of the systems to develop.
My personal vision is to try to keep UML unambiguous and understandable by most, in order to get as many people on board as possible and to address the problematic of the increasing complexity.