A successful synthesis is often a refinement of both sides, which in time might be come to be accepted by both sides as an improvement on the thesis and antithesis, even if there might have been debate initially. That is how the dialectic works. The synthesis ends up extinguishing the synthesis-thesis.
But I don’t think that what @chad is after here, nor is it the main value. Even if a particular synthesis attempt is not successful, the dialogue about it is intrinsically valuable, and end in itself. Even if we cannot agree with each other, the ability to engage with one another is a relational synthesis that’s most people quickly see is better then the quagmire of opposing sides talking past each other, as so often happens in the creation wars.