Biodiesel is a valid point, and I definitely agree we could and should be using more of it. However, there is a large problem with it.
Where are we going to get it from?
It isn't exactly created that efficiently, and quite frankly, if we were to produce enough crops so that we could use nothing but biodiesel, we would have nothing to eat. Hell, we're already faced with an increasing population that food production is struggling to keep up with. Devoting more of our farm land to crops for biodiesel production results in less food for everybody. This of course leads to increased prices, especially beef as corn and soybeans are used for cattle feed, which I'm not exactly complaining about…but it just leads to less people having food. Not exactly good for the future of our Earth either.
As for the cows, I'd love to hear your list of reasons on why having cows is bad.