An "ideal husband" is what we spend the whole play learning not to want. When we're first introduced to Sir Robert Chiltern, he appears to be just that – a "pattern husband," as Mrs. Markby says. He's powerful, rich, handsome, sensitive, and loving. His wife, Lady Chiltern, worships him. When a secret from his past comes to light, Lady Chiltern judges her husband mercilessly. There's no possibility of compromise or weakness. Her good friend Lord Goring has some advice for her: accept humanity, and stop expecting perfection.
Even the secondary characters have some relationship to the concept of "the ideal husband." The socialites Lady Basildon and Mrs. Marchmont would prefer intrigue and excitement; their husbands are so well behaved they are dull. Man-eater Mrs. Cheveley likes her men with a heaping helping of money – and a good reputation on the side. She unconventionally proposes to Lord Goring, who has no interest in becoming her ideal husband. As a free spirit, he gives no inkling until the final act that he intends to be a husband at all.
Is it possible that any of these pampered, high-maintenance people could ever be satisfied by their husbands or wives? For one thing, they'd miss out on a popular social sport in the world of the play – trashing your spouse in front of your circle of friends.
According to Wilde, the ideal husband (or wife) doesn't exist, and to hold out for one is cruel and pointless. As Mabel says at the end of the play, "Oh, I don't think I should like [an ideal husband]. It sounds like something in the next world" (4.290). She wants to be a "real wife," someone with the natural, spontaneous, indulgent behavior she's shown throughout the play, driven by love of her spouse's talents and forgiveness of his faults.