While it is certainly possible to put differences aside and to create an ecumenical religion, it is not possible (history shows us) to create a religion that everyone will agree with.
It is surely possible to create a religion that takes important pieces of various religions and synthesizes them. Almost all religions, for example, teach that all people should treat one another well and that those who have money should help those who have none. The problem is that religions all have to have doctrines as well. It is in these doctrinal areas where it is apparently impossible to satisfy everyone. We can see, for example, that churches as similar as the Church of England and the Roman Catholic Church cannot unite. We have seen tremendous differences between Shiite and Sunni Muslims. It is clear that on a matter as important as religion, people will always find grounds on which to disagree and to split from one another.