A couple comments of relativism from Heidegger's The Basic Problems of Phenomenology. The first on why history itself is responsible for relativism.

It is not the case that at all times and for everyone all beings and all specific domains of beings are accessible in the same way; and, even if beings are accessible inside the range of experience, the question still remains whether, within naive and common experience, they are already suitably understood in their specific mode of being. Because the Dasein is historical in its own existence, possibilities of access and modes of interpretation are themselves diverse, varying in different historical circumstances.

P. 22

This one on why a belief in relativism is justified if one does not already know all the answers.

Has any factually existing Dasein, has anyone of us as such, decided freely of himself and will any existing Dasein ever be able to decide of itself whether it will or will not enter into existence? Never. The establishment of eternal truths remains a fanciful assertion, just as it remains a naive misunderstanding to believe that truth, if it exists only and as long as Dasein exists, is delivered over to relativism and skepticism. On the contrary, the theories of relativism and skepticism spring from a partially justified opposition to an absurd absolutism and dogmatism of the concept of truth, a dogmatism that has its ground in the circumstances that the phenomenon of truth is taken externally as a determination of the subject or of the object or, if neither of these notions works, as some third realm of meaning. If we do not impose on ourselves or surreptitiously permit hidden convictions of one sort or another to play a role in our investigation, then this insight emerges: unveiling and unveiledness--which is just to say, truth--are grounded in the Dasein's transcendence; they exist only so far as Dasein itself exists.

P. 221-222

So, while there are no absolutes, that doesn't mean everything must then be relative and anything permitted, because Dasein circumscribes truth.  ¶ 7:05 PM