You have failed to explain how belief is not a matter of opinion, like which flower is the prettiest. Saying a religion is wrong is like saying that a bird of paradise is prettier than a rose, and at the same time calling everyone who likes roses best wrong.
Religion isn't atheistic or opinion. It correctness isn't subjective. Religion places several things are true, and for most religions, one of the core tenets is some sorta god.
Anything which is asserted to be true must be challenged. From with standing challenge, then can it be given credence.
Each claim of truth of any religion can be viewed independently of the other truth the religion holds. And some religion do have truths, but if the basis for those truth are false, then it should be thrown out.
You can demonstrate that stealing harm others, independent of any godhead. You can demonstrate that killing harm others without a godhead. Hell, you can even demonstrate being ass can harm others.
You can't demonstrate any gods.
Most religion state these are bad because of God(s). When examined, the component of the god adds nothing. And therefore should be dropped.
An example of something getting an idea correct, a truth but from the wrong basis is phrenology. It basis for determining that the brian is compartmentalized is correct, but its basis was erroneous. Thusly it was dropped.
Edit: Hold false truth is harmful. It allows for other false truths to be held, increasing the likely hood of accepting at best waste of time, and worse, the cost life and money.