Here is the whole exchange, taken from Genesis 25:
So, the Bible tells us that Esau was "faint," and Esau says as much and then goes one step further, claiming that he is "at the point to die." If this is an accurate portrayal of Esau's condition, Jacob probably should have just given Esau the food. In fact, he probably should have just given him the food, even if he wasn't that hungry. We have a moral obligation to feed the hungry, but beside this, these two are brothers! Isn't it typical for most families to share with each other? I can honestly say that if one of my siblings asked for a meal, I would make them one, and I wouldn't ask them for much, if anything, in return.29 ¶ And Jacob sod pottage: and Esau came from the field, and he was faint:30 And Esau said to Jacob, Feed me, I pray thee, with that same red pottage; for I am faint: therefore was his name called Edom.31 And Jacob said, Sell me this day thy birthright.32 And Esau said, Behold, I am at the point to die: and what profit shall this birthright do to me?33 And Jacob said, Swear to me this day; and he sware unto him: and he sold his birthright unto Jacob.34 Then Jacob gave Esau bread and pottage of lentiles; and he did eat and drink, and rose up, and went his way: thus Esau despised his birthright.
But let's say that Jacob had some reason to believe that the birthright would be safer with him. After all, Esau clearly isn't a good steward of the birthright if he was willing to give it up so easily. Unless, of course, he was actually starving. Very few things are worth dying for, and a birthright you aren't going to live long enough to enjoy probably isn't one of them. If Esau truly was starving, he might have been justified in giving up the birthright in exchange for a life-saving meal.
But if Esau wasn't actually starving, he was a very poor judge of value. Not many people have traded something of that much value for something of so little value. And if Esau valued his birthright so little, he probably didn't deserve it.
So the morality of this situation hinges on how hungry Esau was. Was he starving, or was he exaggerating? What does it mean that he was "faint"? However hungry Esau was, Jacob probably should have fed him, and it's good that he did, but Esau's selling of his birthright for a single meal indicates either tremendous foolishness or great desperation. I wish I knew which condition convinced him that he should sell his birthright for a little bit of food.