The second is a good reason but not a very strong one, given that there are lots of intellectually interesting things that could be taught, many of which, given limited amounts of time, won't be.
The third is a good reason but again not a very strong one; high school students don't learn much biology and most of what they learn could probably be taught without explaining the underlying logic of why organisms are as they are.
The fourth, I think, is the best reason of all-but the fourth depends on actually teaching the implications of evolution, which is unlikely to happen in public (or most private) schools. To take the most obvious one, evolution implies that we are "as if designed" for reproductive success. Males and females play strikingly different roles in reproduction. Hence evolutionary theory strongly suggests that males and females should have lots of differences-not merely reproductive machinery but distribution of abilities, behavioral patterns, and the like. That prediction is strongly supported by empirical evidence. For a good popular account, see Wright The Moral Animal. But it is an implication inconsistent with a good deal of modern ideology, most obviously the main-but not only-strain of modern feminism.
There are quite a lot of other implications for our species. For instance, theory suggests and evidence supports a pattern for species such as ours, with pair mating and offspring that require substantial care, of monogamy tempered by adultery, with good evolutionary reasons for both the monogamy and the adultery.
While there are surely some people who find none of the implications offensive-myself, for instance-I doubt they make up even a large minority of the population. Hence we are unlikely to see the parts of evolutionary theory most useful to ordinary people-its implications for understanding our own species-taught.
Reference: http://master-of-pentagram.blogspot.com
