Writing homework essay anonymously to avoid controversy
The point of an exercise in dissecting a contentious issue is not that you must agree 100% on the solutions to the issues by the end. The point is to find where you and the other members agree and where you and the others agree either that a) further research is needed or b) fundamentally different approaches are being proposed.

Your desire not to sign off unless you agree 100% with everything in the document essentially defeats the integrity of the exercise. You are allowing your (preconceived) stand to override the goal of finding common ground. Common ground is saying "We agree on these statements, we need more time on these statements, and we disagree on these statements."

So, first compile a document that presents the statements where you both agree, where you both agree that further research is required, and where you both agree that you both disagree.

Then, prepare an addendum. Present your views for the statements where you disagree. Invite your co-author to do the same.

Avoid using the addendum as a way to poke holes in the main document. The addendum should be of the tone "I FULLY agree with the presentations in the main document. I see issues however at the noted points of disagreement. My reasons are as follows: ..." Limit the addendum to a minimum (e.g. one page or even one paragraph).

Submit the document and the two addendum pages.