Belief should not be optional in the face of well-supported scientific conclusions. The problem is it's easy to mistake un-supported conclusions for well-supported conclusions.
I'm fine with anyone who wants to question climate change, evolution or even something as accepted as gravity. Questioning is how we refine our thinking.
Where I get less okay is when people use their questioning to justify behaviors that, should they be wrong, are detrimental to society and the world. Question climate change all you like, but stop polluting until you've convinced the majority of climate scientists. Question evolution, but stop preventing schools from teaching it or forcing them to give creationism an equal standing until you've got something that is, at least, equally supported.
Science rarely does black and white, but you can still get a lot of benefit from altering behavior based on a scientific prediction that is 60%, 80%, 90%, 99% or 99.999% likely/accurate. Forcing belief doesn't honor that small bit of doubt that's inherent in any scientific study. But betting against what science believes to be likely when there are negative consequences to being wrong is stupid and we need to stop doing it.
Question climate change all you like, but stop polluting until you've convinced the majority of climate scientists.
Just because they're all convinced it's completely our fault things are changing, doesn't mean that the prescribed remedies will actually work.
What if the models are wrong on the low side, and we're wasting resources trying to stop the inevitable when we should be figuring out how to survive it?
What if I don't trust the scientists doing the work, or the larger system that they work in? What if I find the common incarnation of the entire field lacking? I do not trust much published by sociology, regardless of how many studies show results, because of the political nature of the field.
On the other hand, physicist who say they found a new particle? I don't have an once of doubt (though maybe I should have a little).
Part of the problem is that the very language used in sociology is crafted to reached the desired findings. Once the integrity of an entire field has been lost, what can be done to restore it?
Technology is created based on using facts discovered by physicists - layer, upon layer, upon layer of very precise and constant use of fundamental ideas of physics. If unexpected things keep happening, it gets investigated and sometimes "new physics" is discovered.
On the other extreme (of what some call science) there is the social sciences and psychology. A study with a p=0.05 (95%) claim to being true. Lots of problems with p-hacking and replication. Scientific experiments are either unethical or impossible.
Here is a cute cartoon about the spectrum (https://www.xkcd.com/435/), although I would title it, "Fields arranged by certainty of truth". I work in geology research where the certainty of truth of the ideas/theories we promote vary across the whole range. This can be quite fun, but one needs a very well developed sense of how true the ideas you hold are to make progress.
The subtleties on the probability of an idea being true and over which domain it applies to is why people consult "experts". Hard to choose an expert when you are not an expert.
C'mon, use logic and reason.
What does that mean in real terms? What do you propose doing to those people who take the option of not believing? If the answer is nothing then belief is indeed optional.
I suppose there's ostracism for a non-state solution. So if you're a business, maybe once a year you make all of your employees measure some toads, and if they can't apply a Kolmogorov-Smirnov test correctly on the first try they're immediately fired and added to a shared blacklist.
How exactly are you handling enforcement?