I have not actually seen it (and I'm not the OP), but I have been told by French farmers that geese
do willingly and even eagerly run up to get the tube inserted so that they can have the food force fed into their gullet. At least with the few farmers I've talked to about this, the tube was not inserted permanently (these were very small operations). Having never actually seen it, I don't have any understanding of the discomfort the animals face or the extent to which these reports are true. But neither do I have reliable information that it is not true.
Disclaimer: I don't eat foie gras and don't advocate it either.