Often sacrifices have to be made. Syncretism will allow society overall to leave in peace, but at the expense of peoples freedom. Take a look at United States. It has hundreds if not thousands of languages and culture, and they seemingly work very well. So it is possible to leave in peace, as long as there is a compromise between its citizens.
A puzzle is not a challenge when all the pieces are square or triangle. A puzzle is better when the shapes are different. It is more satisfying to complete a puzzle that was a challenge as opposed to one that was solved quickly and easily. The same works for a society. When a nation is built on the premise of diversity rather than in spite of it, the end result is more appreciated by all.
Syncretism is defined as the combining or attempted combining of different religions, cultures, or schools of thought. I believe combining cultures and schools of thought can play a role for a society to live in peace, but when it comes to religion I don't think this method works as well because people usually hold onto their own set of beliefs very sternly. When it comes to religion and peace in society, tolerance is probably of utmost importance.
Syncretism has a large part in allowing society to live mostly in peace. If you weren't able to bring conflicting ideas together and form some sort of medium, we would be at each other's throats all day every day, and there would be no end to the chaos. This is vital.
No, I do not think that this helps out with keeping a society to live in peace or not. I think that for a society to live in peace they have to have a good and strong government that treats the people fair and gives them plenty of human rights.