The word "had" there serves an important point, contrast this with the fact that people don't have to live with other ethnic groups.

Yes, but it could also imply that women are difficult to endure, and men would be better off without them. But of course this meaning was unintended, thus the humor.

Yes, they do. If this wasn't the case we'd still be on the savannah getting chased by lions.

But where does the selective pressure comes from? Why this pressure has not made the atomistic idea, or the spherical Earth, formulated almost three thousands of year ago, immediately popular? Why there are people that still believe in magic? Why we still believe in both relativity and quantum mechanics, despite these ideas being incompatible and more than a century old?

Um, tribes have to compete with other tribes. Memes can't survive for long simply because they aren't immediately destructive.

Yes, avoiding to be immediately destructive is not sufficient to guarantee a meme survivability, but cultures can lock all kind of memes if there's no immediate selective pressure against them.
For example, a society that has to battle on phyisical grounds, with physical strength, gains no immediate disadvantage over a more egalitarian society if it enslaves women.
A false meme can even gain a society some advantage, such as the case of an ethnic group that enslaves another ethnic group and makes them work for hard labor.
Past history was about guns, germs and steel, not about truth. Those are what has been selected. The rest of the memes are purely random junk.