Religious oriented claims or beliefs can be mere opinion. They can also be grounded in truth - as is the case in every other domain of discussion.

Let's take the claim that "I believe my dog will be in heaven." There's no way to point to any kind of empirical evidence for that. It's definitely in the category of opinion. But...

When it comes to the statement "There is a heaven," that can be more than mere opinion. It's certainly possible that you may have someone spouting off commentary without ever looking at any evidence, and that's definitely then in the opinion category, but...

What if you have someone making a case for heaven or at least some kind of after-life based on the vast number of Near Death Experiences out there. Indeed, there are many who make just that case. Whether you agree with their argument or not isn't the issue, the point is that we're talking about more than opinion. We're talking about an evidence-based argument that may or may not be true. Not merely an opinion.

And there's something else.

If you write down a number on a piece of paper and ask me to guess, my guess may be just that. But that there is a number written down is NOT in the opinion category.

Religion is ultimately in THAT category. We're talking about beliefs and claims about truths that are often hidden or at least dim or blurry. This is where trust comes in, and it's why there are so many disagremeents. But it doesn't relegate all of religion to simply opinion.