I want to push back against this somewhat, even though I know that maybe isn’t the kind of interaction you’re really looking for with this perhaps, but maybe it’s still better to do that than say nothing, since it’s just my honest reaction—I know I wouldn’t really want to just be ignored if I posted something like that…
Natural selection is a simple, crude process, even if it has complex outcomes, but also, it never selects for better fitness in any kind of general sense, only for suitability to the current environment, which is constantly changing, so there really is no general better fitness. Evolution is more like a drunk meandering in the dark than a continuous climb upwards to the top of a mountain. 
My favorite way of illustrating this is to give the example of a population of bacteria which have heat tolerances of between 35–45°C, and can only tolerate temperatures within 10°C of their maximum. If you heat the environment of this population to 40°C, some of them will die, and you will be left with a more heat-tolerant population of bacteria. That’s natural selection at work. However, if you cool the environment to 30°C, some of the more heat-tolerant bactera will die, and instead you will be left with a more cold-tolerant population of bacteria. That’s also natural selection at work. So, we can really only talk about how well the current population of bacteria is capable of adjusting to their current environment, not how much more fit they are in general, and certainly not how any individual bacterium is more or less fit than any other in any general sense.
Also, I think it’s worth noting that if we started with a population of bacteria which could only tolerate temperatures within 35–40°C, then heated the environment above that, they would all die and the population would be gone. Same way as if we started with a population with maximum heat tolerances between 40–45°C and then cooled the environment to 30°C. So, the diversity of heat tolerances in the original population does give the entire population a certain kind of evolutionary advantage, because it means that some inviduals will get through even if the temperature fluctuates fairly widely.
In general, a population of organisms will benefit from diversity—in their genes, their behavior, whatever—because it means that whatever changes occur in the environment, some individuals will make it. So, if you value human life, diversity is good; it’s good if people have a wide variety of beliefs, if they have a wide gene pool, if they have many different customs and practices, etc. etc.
I don’t think it’s really fair to say from this place that it’s “evolutionarily advantageous to reject other people’s preferences as ungrounded in truth.” Human life is not necessarily a competition—in many ways, we sink or swim together, and we all thrive more when we can all work together more effectively. But, also, I think, in evolutionary terms, it’s better for people to live and let live so that the whole species has the widest span of preferences we can reasonably support. There are many cases when a small group of people with odd preferences turn out to be just the ones we need for some task, or deepen our understanding of what human behavior can involve, or lead to unique art we wouldn’t otherwise have, etc. etc. All of these things make the whole society healthier and more robust. Also, in times of disaster, you never know what kinds of skills and habits will come in handy; there are many different kinds of disasters and some we could never foresee, so having a lot of different sorts of people helps to hedge our bets.
As such, I don’t think there really is any such thing as “disadvantageous truth” full stop. There are beliefs that it may hurt you to hold in a given social context, but in a different social context, they might be rewarded. In general, I think we should strive to support a wide diversity of beliefs in any context. Some beliefs lead people to harm others, and we should perhaps discourage those, but in general, I think we should work to make the social contexts we swim in more hospitable to a variety of beliefs as much as we can without hurting anyone. This will make our social groups more flexible and adaptable, able to meet a wide variety of challenges. If anything in human culture can be clearly said to be evolutionarily advantageous, I think it’s that.
I hope you’re doing okay out there. I’ve been struggingly a lot lately with the feeling that our society is controlled by people who are indeed intensely self-interested and happy to harm others if it suits them, and that too many other people are too resigned to this for it to ever change it or even to help each one other effectively to withstand the harm; I think like, if I was to totally give myself over to that belief, and especially if I was also to conclude that it was inevitable and would always be that way, I would really fall into total despair and give up. So, I’m trying really hard to resist that idea; to some extent I’m speaking even to myself in those posts. I know it’s maybe not exactly the same as what you’re saying, it just sounds kind of similar; I wouldn’t want you to go the route of total despair either, although I know maybe the kinds of arguments I was making don’t necessarily help very much if your feelings are tending in that direction.