In Act I, what is ironic about Kate's question of complaining about what you can see in The Miracle Worker?
In the scene in question, Kate has been trying to persuade her husband to allow her to write to Dr. Chisholm, who is reputed to have cured "lots of cases of blindness people thought couldn't be cured." Captain Keller is not amenable to the suggestion; the Kellers have consulted a number of doctors about their daughter Helen already, only to have their hopes dashed every time. Captain Keller does not want his wife to write to Dr. Chisholm, believing that she is only setting herself up for yet another heartbreak, but Kate is insistent. The Kellers' son James breaks into the conversation at this point, suggesting that the family should send Helen to an asylum; he says it would be "the kindest thing." When Aunt Ev, surprised at his words, chides, "Why, she's your sister, James, not a nobody," James retorts callously,
"Half sister, half mentally-defective, she can't even keep herself clean. It's not pleasant to see her about all the time."
Kate, aghast, reprimands her son, "Do you dare? Complain of what you can see?" She is pointing out the irony in the fact that James is complaining about how seeing his sister's slovenly appearance is offensive to him, when he should be thankful that he can see at all. Helen, about whom he is complaining, can't see; she would no doubt be ecstatic to see even the unpleasant sights about which James has the audacity to fret.
Another way that Kate's comment is ironic is because of her own perception of Helen's behavior, and how her own reactions contribute to it. Kate sees that Helen is out of control, but she does not see that her permissiveness is a contributing factor to the problem.