The reasonableness — indeed, the profound wisdom exhibited over and over again — of what Jesus said should be a powerful apologetic tool, should it not? That is, if Jesus’ teachings are godlike then it is evidence that He is indeed God. Conversely, if He consistently talked rot that would undercut claims of His divinity.
It is remarkable in this regard how seldom people, even nonbelievers (pace Nietzsche), will criticize the substance of Jesus’ teachings. It is rare that anyone says, “I’m not a Christian because Jesus said such-and-such and that’s crazy.” It’s much more common to hear, as C.S. Lewis describes in his famous trilemma, someone saying that, oh, sure, Jesus was a very wise teacher — but then denying implicitly or explicitly that He was God.
Jesus’ injunctions are more likely to be viewed as difficult rather than wrong. And of course they are difficult, as any Christian will freely admit — especially the injunctions that require us always to think (as well as act) purely and always to act affirmatively with love (and not just refrain from hurtful acts). Recall that, when accused of not “caring for” the Sermon on the Mount, C.S. Lewis replied: “As to ‘caring for’ the Sermon on the Mount, if ‘caring for’ here means ‘liking’ or enjoying, I suppose no one ‘cares for’ it. Who can like being knocked flat on his face by a sledge hammer? I can hardly imagine a more deadly spiritual condition than that of a man who can read that passage with tranquil pleasure?”
By the way, I think that to the extent that people do reject Christian teachings on how we act, it is with regard to what I heard Ryan Anderson once describe humorously as the “pubic issues” — that is, things like abortion and gay sex, as well as fornication generally. Given that, one suspects that perhaps selfish hedonism is playing a role rather than just cool philosophical reflection.
Caveat: The fact that Jesus may not always have the same rules as we would is neither disproof of His divinity nor, for the Christian, a justification for not following them. And if you think God was profoundly wise and right about everything except gay sex then, well, maybe you should entertain the thought that He was right about that, too.