Re: Why is bacon "processed"?
Preservatives are there to, er, preserve stuff, which is the opposite of why you eat it - your body needs to break it down to use it. You may as well eat flavoured sawdust. You'll be full, but malnourished and you'll be putting a strain on various systems which deal with breaking the food down. The commercial imperative for long shelf life reduces the usefulness of the food.
Additionally, processing food often leads to changing the nature of what you are eating. So peanut butter may be made from just peanuts, but probably not in their natural ratios of oil to protein. Soy milk may be made from just soy beans and water, but usually its just the soy protein which has been extracted from the beans (because the beans themselves taste nasty) and bound with the water molecules (otherwise they'd separate in transit). The problem is that you may be consuming things in unnatural quantities, which puts a strain on your body's systems - too much fat, too much salt, too much sugar are common culprits - they are cheap to produce and yes, they do taste nice.
Meat is a very efficient way of consuming stuff, but stuff can be good (nutrients) or bad (poisons, fats). Animals are just a way of processing the veg before consumption. Problems increase when your animals aren't given decent things to eat or are otherwise rendered unhealthy. It gets worse since meat is more difficult to preserve than vegetables and poor diet (feeding sheep to cows) is easy to disguise. The meat industry also attracts subsidies for production which skew the market costs of food. The upshot is, the less processing is involved, the less likely it is that someone has messed up your food.
Diet is complicated - too complicated to be definitive but there are some generalisations and lessons to be learnt from statistics. Sometimes, by imposing broad guidelines you can avoid specific but common mistakes. For example, you can eat lean meat from healthy sources. However, going vegan means you cut out most of the sources of excessive fat available and can steer you away from a lifestyle-induced heart disease, which is the main cause of premature death in the West. It isn't just dropping things which helps. I've seen plenty of fat unhealthy vegetarians gorging on cheesecake. Dropping the meat isn't helping that much. However, not relying on meat for your nutrients can be a way to force yourself to look at consuming a wide variety of fresh veg, not just mushy peas from a can. Consuming fresh veg with lots of natural colours, not just white stuff, is good for you. This is why non-gmo is important - we don't want to be duped into eating unripe food by genetic shenanigans.
Personally, I've found that incorporating more raw/barely cooked food and whole grains (e.g. wheat rather than flour) into my diet has provided a lot of benefit. Its extremely planning-intensive, but the results are delicious- which is my main motivation. That's not just raw broccoli, but creative ways of using seeds, nuts and dried-fruit for filling food in tiny portions, compared to say, pasta (which usually implies cheese) which I would normally consume in huge portions. I could do a healthy pasta, but I'm more likely to dump a cheese sauce on it, or use the cheese I bought for it on toast instead. Like awkward change-control, the aim is to force myself to plan properly, rather than try winging it.