"Scientists have known for *decades* that there is a measurable intelligence difference between men and women." - i know that in the 80s there were tests of mathematical ability, basically the top 1% of people based on math scores were male at a ratio of ~ 13:1 (13 males for every 1 female)
This study was repeated about 20 years later, and it was found that this had changed to something like 3:1... it turns out what they were testing was not people's raw ability, but societies preference.
You can see this be repeating the test in other societies and getting different results. The US appears to have become less sexist when it comes to maths, and the jobs which you can get from them over the past 20 years; though not as far advanced in equality as scandanavia and iceland - where the got scores with females doing better than males.
There is a definite social impact on learning. We know this, and if you tell kids growing up that they can only be a certain type of person, they will not invest the intellectual effort required to excel in other areas, (except perhaps that 1 in 13, who do it despite what they are told...).
Beyond that, it has been known for decades that IQ tests are limited tools. They tell you more about the person designing the test, and what they value as important skills than they do about intelligence. They are a measure, just like running speed; what importance we place on running speed is about society, not the value of a person.
The same is true of IQ.
Black people disproportionately end up in prison in America, does that evidence tell you that they are naturally inclined towards breaking the law?
Studies seem to show that white and black americans use cannabis at about the same rate, yet more black people are convicted - that just tells you about the way the law is enforced.
'If it were as easy for gay couples to have children as straight couples, however, I feel they would be significantly worse (a loving and dedicated couple with male and female experience is the clear ideal), but as it won't happen it's a moot point.'
- as it happens it will soon (probably within our lifetimes) be possible for gay couples to have children. And at that point what arguement will you have against them raising those children, made from their own genetic material, they would have exactly the same claim to them - the free market dictates this technology will become available (though i don't know what it will cost) and there is a tonne of research being done on fertility which will help make it happen (including a recent breakthrough in three-parent babies, which is an amazing achievement in itself)