It is clearly possible to say that someone like Hitler was wrong in moral terms
without reference to religious dogma or political ideology.
Do you think that all values are subjective?
It depends on what you mean by subjective. Subject to different human beings? Subject to different societies? Subject to different species? If you choose your definition of subjective to mean subjective within the human race, I would say that we all share some fundamental values (i.e. human life, especially friends and family). We all like different types of music, movies, and books, and also differ with respect to more important values like our hobbies, political values and religious values, but human life is something that nearly all of us value as it is programmed into our biology. We are programmed to value our lives, and the lives of others, and I would consider this a universal value. We can see that it is valued across different cultures. Cultural values are largely reflected by the laws effective in their respective political system, and as nearly every civilization has penalties for taking a human life, we can deduce that they all value human life. Along with human life, every culture values knowledge, morality (in various forms) and social order, as reflected in their educational and political systems. There are other values that are widely shared, like civil liberties, legal equality, property rights, freedom of thought, individuality, etc., but these aren't reflected in all societies and are even discouraged in some. I believe that the majority of our values differ depending on our culture and our personality, and that human life, morality and knowledge are the only true universal human values shared between cultures and individuals.
However, this raises a question...are these universal values anthropocentric? Well, let's look and see if other animals can even have values. One definition of value is simply "a liking or affection". Using this definition, values can operate at the instinctive level, below the realm of conscious thought, and we can say that other animals have values as well, but not necessarily our same values. I don't think that a pig values a human life too much, nor does a horse. I'm also not so sure that an ant is concerned with knowledge or morality, being too primitive to conceive of such a thing. Are there any true interspecial values? The only one I can think of is existence. Every creature values its own existence, and will try to preserve it unless there is an altruistic motive to die, with the exception of suicide in humans (it's possible that there are motives to this at a genetic level, but it's too complicated to elaborate on).
Edit: When I speak of universal values, I don't mean values that are shared by every single human being, just values that are shared by the vast majority of human beings.