Buddhism has a "wide spectrum" because it's not an authoritarian religion. Whereas Christianity is about avoiding sin, Buddhism is about avoiding suffering. Ultimately Buddhism is about being a good person. It doesn't have a concept of good and evil, which are theistic concepts, but enlightenment and ignorance. People do bad because of ignorance. Buddhism, thus, is simply about enlightenment.
Buddhism is generally described as an atheistic religion, just like 5 of the 6 schools of Hinduism. Buddhism doesn't care about your beliefs. You don't have to be a Buddhist in order to become a Buddha.
Buddhism is only vague if you need need to be told what to do. That's what the Buddhist texts are for. A guide. If you don't need them in order to be a good person, all the more power to you.
Actually, the texts may not say. The moral system of Christianity is duty ethics. God commands and it's your duty to comply. The moral system of Buddhism aligns with virtue ethics. Which simply can be described as being good for goodness sake. It aligns with Aristotle's virtues life. I'm not a scholar, but this seem to reflect virtually all pre-Abrahamic or pre-Christian religions/philosophies. Buddhism is a very typical religion. It's Christianity and the Abrahamic religions that are atypical.
With that said, things generally follow. The Catholic Church opposes contraceptives because it follows. Lust is one of the 7 deadly sins. Sex for any reason other than procreation is lust. Contraceptives are a means to sin. Masturbation is denounced for the same reason. I'm not arguing right or wrong here. This only illustrates why the Catholic Church hold this position. By the same token, it's easy to understand how vegetarianism follows from avoiding suffering. We can also understand how contraceptives can reduce suffering.
It goes without saying that the followers of a religion may not necessarily follow the teachings of the religion.