JWs (probably accidentally) really managed to instill in me a love of truth. I took that part really literally when I was younger, and it may have something to do with my love for science and learning that has persisted down to this day. So it's primarily on that basis that I object to religion. It generates in me no small measure of disgust when I encounter someone purporting to dispense truth to followers, when they really have no way of substantiating their claims.
The usefulness of the ethical (or, perhaps, less unethical) versions of religion out there is something that I often find difficult to pin down. I'm tentatively settling on the comparison to the many heuristics that humans use in thinking, for example, the availability heuristic - estimating the likelihood of an event based on how easily you can call to mind an example. This was once probably very efficient ways to get really close to the truth, but due to the many layers of selection bias in our modern society (i.e. what gets reported in the news, what gets talked about in the office, etc) this heuristic now leads people to greatly over-estimate their likelihood to get murdered or die in a terrorist attack vs dying from heart disease or a car accident.
I now mostly view religion in this way - in the past it was a powerful force for bringing together a tribe and focusing people on the collective good of said tribe, especially in times when scarcity and violent conflicts with neighboring tribes were common. But in modern society we've gone a long ways of figuring out things like efficient land use and diplomacy that have driven religion to obsolescence in these areas, and worse it can often be a hindrance. In some places, maybe in driving local community involvement, it can perhaps still be an effective tool that has fewer drawbacks if its tendency to drive tribalism is kept in check - in much the same way that the availability heuristic can be very useful if we are careful not to apply it to things that have undergone the filters of selection bias. All that said, though, it is also true that there is absolutely no occasion where, given the choice, the availability heuristic would never be the best approach to estimating probability if you had the time or mental resources to fully take into account all the data at hand and rigorously analyze it with properly developed (Bayesian) statistical tools. I see a strong parallel here for religion as well.
Religion is often used as a shortcut to meaning - do these things and you will have lived a good life. In my view, constantly examining your life, motivations, intentions, and your actions and their outcomes, is a far more effective and generally applicable way of leading a good life. In just the same way that heuristics have zones where their not applicable, but the full theorems of statistics don't, so too does religion have holes - rules listed as a path to a good life often include things that are unnecessarily troubling (e.g. excessive control on sex, excessive reliance on gender roles and male authority, etc) that the generally applicable principle does not (I make no claim that I've discovered such a principle, just that it likely exists). But at the same time it's easier to say "don't have sex unless you're married" than it is to teach someone the risks of having sex, how to mitigate them, and how to respect your partners and your own emotional health in the process.
So, all this said, I'll admit that (non-cult, friendly, less unethical) religion is likely useful in some cases. The biggest problem with it, in my mind, is that it doesn't encourage the religious to recognize when their religion isn't useful. If people could simply realize that their religious rules might have exception, or might lead to erroneous scientific beliefs, unnecessary tribalism, or rules that might be injurious to some, it would go a long way to eliminating most of the problems that I attribute to religion. But, I suppose, if people realized that their religious dogma could, even in principle, fail them, then it would cease to be religion.
