Religions persist in spite of modern knowledge

Yes mankind would be better off without religion, but that is not likely.  Religions have tricks to keep themselves going, and those with the best tricks last longest.  If only people could see the tricks involved in ideas like faith and loyalty when applied to myths, but once one has been indoctrinated (usually as a child), only some have the personality traits enabling them to escape, and indoctrination is a form of addiction, not easy to break from and very easy to find excuses for not wanting to break from.  

Why don't gays die out?

A comment on this gay business: my understanding is that at least for male homosexuals the tendency is inherited in the female line, perhaps even on the Y chromosome (although of course the idea of a gay gene is too simple).  If that is the case, even if gay men don't reproduce, it would have no effect.

I would agree that strictly gay men almost certainly don't have babies, unless they do it medically, and most won't.  That may be evidence that a "strictly" gay man is much more rare than imagined.

Another possibility is that gayness provides some unrelated survival benefit, such as better survival rates in the womb and in childhood, and maybe even in finding a wife.  For gay women, it has been so long that men dominate that they just go ahead and have babies, until recently at least.  

Sources of knowledge

I think maybe we can imagine four ways of obtaining knowledge.  First is to be born with it (evolution supplying us or something like that.  Problem is evolution is only interested in propagating our genes so the information we are born with may have survival value but not much else, and to a large extent this will be things we know but don't know we know.

Then there is standard deduction -- starting with things we already know and deducing further knowledge from it.  The problems here are well known -- the logic may be wrong or the things we "already know" may be wrong.

Then there is induction.  If we see something happen over and over with no counter-examples, we infer that it is a rule of the universe.  Of course this is what science does, but we all do it too.  It has the standard problem that it may be we just haven't yet found the counter-examples.  It is collections of such rules about a related subject that scientists call "theory."

Finally there is the way most of us get our knowledge -- by getting it from an authority on the subject.  Experts know more than we do so when we want to know something we go to them.  I think in this general category there is also getting special revelations from supernatural beings or from ancient writings.  This makes clear the problem with this method of learning -- we have to chose our experts carefully.