If you're concerned about family farms you would oppose things too like ag-gag laws regarding un-hygenic food production/abuse and the general anti-humane industrialization of food products both animal and other.

These are far more potent threats to traditional pastoral and agricultural traditions than tax policy. If it was just a bunch of family farms competing against each other (or more likely forming co-ops given history) then it might be a bit more of a fair playing field.