Raising livestock en mass is also very harmful to the environment.
Of course, this is already a big problem for the future. Mass production of animal products brings a lot of problems. Where you have a lot of animals, you will have to deal with diseases of all kind. Especially chickens or turkeys from a big farm are often not much more than antibiotics and other immunisations cocktails because so many animals at one place are a big incubator for diseases.
Also you have to consider that the population is growing and so did the demand for these animal products over the last time. Animal manure and animal emissions have an impact on our environment, for example a cow produces lots of methane gas (CH4) which is about 20-times more dangerous for the climate and ozone layer than CO2. But CO2 is the much much bigger amount, so CH4 by cows is only a very little piece of the overall effect. But still, these are all little pieces.
Buying locally may be the only way to truly combat this system. I have tried to do this more often lately --- but it's not easy to stick to that mantra.
I also try to do this as often as I can. But you don't have the possibility to buy local bio food everywhere and plus I also want to enjoy some food where I can't avoid that I will not know from where it does exactly come from. Also another factor not to forget is the higher price. If you have enough people who are struggling financially to manage their living, you won't get them to buy something which costs around 50% more.
A completely different point I want to add is referring to "I only eat what I cook" somebody said above. This is the ideal solution if you can do that, but I think our society in most countries became too different to realize this. Too many single households, and if you have a family, too often -even in ordinary middle-class families- both parents have to go to work to earn the living. And who comes home from work in the evening, is maybe tired from the day, just wants to relax a bit, to cook him/herself (alone?) a nice, but very time-intensive meal with fresh and natural ingredients where nothing was prepared. And what are you doing during your lunch break when you are at work? Usually you should have the most important warm meal of your day at this time and not in the evening.
It's really difficult to pay attention to these important things.