That’s because in the old world, social cohesion was the most important factor in your group’s survival. Anything that got in the way of that, like neurodivergence, being otherwise different, or not having children with other members of your group when it was expected, could endanger your survival*.

Thankfully, we’re not in that world anymore, and the differences between our world and the one in which those rules/laws arose are what make morality developed during that time irrelevant. We can explain why murder is still wrong today without relying on religious texts for justification, but we can’t explain why eating lobster is more wrong than eating beef anymore, nor can we explain why just being different is wrong anymore.

The people who made those laws lived in a rapidly desertifying climate before refrigeration or indoor plumbing - if your group wanted to eat lobster, they would have a lower chance of survival overall. You can find reasons like this for most religions’ rules, and some of them, like banning murder, still contribute to our group survival, but that’s not a reason to assume any given religious prohibition is sensible today.

*to be clear, I’m not suggesting that any of those things were actually wrong or inherently contrary to a group’s survival, because many cultures had no issue with weirdos, neurodivergence, or queerness. The people making these rules probably believed they were good for their group, but they didn’t have access to the information that we do now, nor did they have the benefit of the intervening millennia of philosophical developments. The groups that prohibited queerness and observed dietary restrictions were also trying to separate themselves from the groups around them, to strengthen in group feeling, and they enforced it later when converting new groups as a way to mark a clear cultural shift from the old ways.

First of all "tend to be" and also they are not that old believes for the most part. You have to keep in mind that for most of human history we have been hunter gatherers and they did not practise slavery for the most part. They would also understand that black people, as human beings are animals, but that women are humans. Jews are pretty new anyway. Gays would have been mostly seen as natural(it actually has a lot of history of being seen that way)

We know that our current agricultural system is in long term trouble. As in it depends on fossil fuels for fertilizers, uses a lot of poison, which destroy the natural support system and destroys the soil. We know that fossil fuels are going to run out and that at that point we need the natural support systems and good soil again. However as a society we do basically nothing about it. Hell our current best attempt at a new idea solution is to burn a hell of a lot of fossil fuels to run some giant AI data centres to somehow solve it, without actually having any sort of idea how exactly that is going to happen. Again the very fossil fuels, we know are going to run out.

Compare that to sacrificing a child for better crops. That did not happen every year, but when the group was worried that a crop was going to be bad. At that point it removes a person, which the group has to feed, which makes it possible for the group as a whole to survive. The religious part is done, so the people feel better about it. Certainly a hard choice, but a better one the collective suicide, which is what we are going towards today.

and none of that is an argument to say: old believe = bad believe

Also:

Europeans still think colonization was actually good for the colonized

https://www.statista.com/statistics/1103250/people-s-opinion-on-former-colonies-2019/

In most places, “traditionalists” claim any raped woman wasn’t actually raped

Rape is similar to murder widely accepted as a crime. There are obviously cases where that did not happen, but still basically everybody considers rape to be wrong.

the USians still think their country is the absolutely first and best in the world, or at the veary least a 1st world nation in the development sense.

Only 25% of Americans believe the former