There are many instances in which the most conservative usage is to refer to a person using “that”: “All the politicians that were at the party later denied even knowing the host” is actually somewhat more traditional than the more popular “politicians who.” An aversion to “that” referring to human beings as somehow diminishing their humanity may be praiseworthily sensitive, but it cannot claim the authority of tradition. In some sentences, “that” is clearly preferable to “who”: “She is the only person I know of that prefers whipped cream on her granola.” In the following example, to exchange “that” for “who” would be awkward: “Who was it that said, ‘A woman without a man is like a fish without a bicycle’?”*

*Commonly attributed to Gloria Steinem, but she attributes it to Irina Dunn.