Gallimard has both sympathetic and unsympathetic elements. He commands the sympathy of the audience because he has grown up, by his own admission, "the least likely to be invited to a party" (Act I, Scene I). He knows that he has never been considered smart or clever, and he is now jailed in a cell that is four-and-a-half by five meters. The partygoers in Act I, Scene II refer to him as not very handsome, and the woman in that scene says that she feels pity for him. He is clearly a sad character who has long wanted to prove his worth.
On the other hand, Gallimard has been infected with the poison of colonialism, which makes him willing to exploit Song. As he says in Act I, Scene III, "the Yankee travels, casting his anchor wherever he wants." In the part of Pinkerton from Madama Butterfly (the opera by Puccini), he relishes exploiting the lands his nation conquers and also feels that he has the right to conquer its women too. Therefore, Gallimard is both perpetrator and victim in this play, and he is deserving of sympathy in some ways—but not deserving in others.