Why did they hunt humans?

A smarter way would been to work the with humans, give them land so they could breed and multiply, blood after all is a renewable resource there could have been clinics all over the country where people walk in give blood get paid, like they do now. Come to think about it a vampire communtiy would actually be pretty good for the economy, humans run the coutry during the day and the vamps at night imagine america running 24/7 even more so then it is now imagine the productivity. They only drink blood so we dont have to worry about food shortage, blood would become a hot commdity people could get out of poverty just by selling there blood. But since vampire arent real this is just rambling, but either way i enjoyed the movie 7/10 it not perfect but i really cant find anything to complain about decent movie.