I'd say that vetos are clumsy. It's too easy to abuse them instead of communicating. Some established couples get into this habit of vetoing each other's other significant others, causing a lot of unnecessary confusion and lasting resentments (in the established relationship). It's the same explanation for why the United Nations is a big joke. Vetos privilege certain people and relationships over others. The impulse to 'protect' our attachments to property and people is ingrained possibly in our natures and cultures. A better approach would be for everyone to sit down and talk, but that would require so much *hand on head* work.