The Lindner character, although basically a "flat character," is still developed by Hansberry as a human being and not simply a stereotype of a bigot. For example, when Mr. Lindner arrives at the Younger household, he is extremely shy and timid, not threatening or abrasive or loud. He is polite and mannerly even though everything he says is insulting to the Youngers.
It is immediately apparent to us that Mr. Lindner is not even aware of his insults to them. He is simply a courier from the Clybourne Park neighborhood, bringing a message to the Youngers that he, himself, had no part in originating. He has been sent by the organization which he represents, and he naively believes in the correctness of this organization. But never do we get the impression that Lindner is filled with hatred that would make him knowingly insult the Youngers or hurt them physically in any way. Lindner does not realize the scope of his mission. When he says that "people want to live among their own kind," he firmly believes that he is doing the Youngers a favor by offering to pay them not to move into Clybourne Park.
The Youngers are kind to Lindner when he first enters their apartment, and Lindner's amazement turns into discomfort. When they offer Lindner refreshments, he declines because he realizes at this point that the Youngers are decent people, which makes his mission uncomfortable for him. Lindner appears almost pathetic as he tries to explain his point of view to a fiery Beneatha, an angry Walter, and a surprised Ruth.