Well I agree with you - which is precisely why we should have a functioning and fair system for adjudicating claims, establishing facts, and evaluating the merit of various arguments.

One can and perhaps should imagine a more collaborative model of justice, but our current model is adversarial and, arguably, gladiatorial. Both sides present the strongest possible version of their case - intentional misrepresentation by prioritizing favorable context/evidence and ignoring, minimizing, or calling into question damning context/evidence is by definition what each side is supposed to do. By aggressively pursuing each party's interests to the extreme, neither can say they didn't receive a robust and fair hearing of their position. In fact, they had the best possible representation of their position and very likely better than they could have formulated on their own. Then the jury or judge weighs the merits, truth, and context against each other and determines which side is more trustworthy/meritorious. That can include punishment for perjury if either party knowingly lied.

To pre-assert that some people are not allowed to make claims in their own defense is wildly out of line with any presumption of innocence until proven guilty and immediately likely to result in further abuse of the most marginalized.