There are different classes of food processing, with very different properties.

The kinds of food processing methods that remove from raw food the parts that are unhealthy or undesirable cannot have in principle any kind of harmful effect, when the processed food is used correctly. They may have only an indirect harmful effect because the availability of pure food ingredients may enable some people to use such processed food in an incorrect way, by making food that has an unbalanced composition, for instance food that has too much sugar.

On the other hand, the food processing methods that cause irreversible transformations of food, i.e. mixing various ingredients and/or using certain food treatments, e.g. heating, are quite likely to have harmful effects on food quality, when they are done in an industrial setting, instead of being done at home. The reason is that an industrial producer has very different incentives than those who cook for their family, for friends or relatives, or at least for some loyal customers who appreciate good food. An industrial producer cares only for the appearance and taste of the food, and for its production cost. So any useless or even harmful ingredients will be used if those reduce the production cost, as long as the food still looks appetizing and it has a good taste provided e.g. by excessive sugar, salt and bad quality fat.

So the problem is less that food processing methods are bad per se. The problem is that most producers of processed food cannot be trusted to use processing methods that are good for the customer, instead of being good only for the producer. Now there are a lot of regulations that prevent some of the most harmful methods of food adulteration that were used in the past, but they are still not severe enough to ensure that every producer makes healthy food.

> The reason is that an industrial producer has very different incentives than those who cook for their family, for friends or relatives, or at least for some loyal customers who appreciate good food. An industrial producer cares only for the appearance and taste of the food, and for its production cost.

Now I'm not denying industrial players have a different set of incentives than people cooking for themselves, but it's not all evil either. They also care about appeasing regulators in countries where food regulations exist, and they may care a bit personally since they themselves and/or their family is eating that too, so I wouldn't necessarily paint them as completely disconnected from the rest of society.

Now, on the other hand, the industrial producers have a few more things going in their favor, such as they actually have quality control metrics, and they are in actual position to make good on caring about food. Home kitchens are not, regular people have neither knowledge nor appreciation of the complex chemistry involved, and even if they did, the equipment used in home kitchens is too crude to allow for consistent quality (not that we can hope for any with no supply chain control either).

(The slightly-fancy restaurants are arguably the worst - they combine all the bad incentives of a high-volume, low-margin commercial operation, with equipment and setup inadequate to guarantee any kind of process quality control. Contrast that with e.g. McDonald's - they may be serving mediocre food at best, but they do it with engineering precision, and you can be sure they aren't just microwaving you an old chicken breast and adding burn marks with an electric grill to make it look like you'd expect for a $50 menu item with a name written in French.)

So the irony is, the industrial producers may have misaligned incentives, but they're also the only ones in position to deliver actually healthy and quality food. Regular people have neither knowledge nor equipment for that, and all the "healthy eating" fads abusing real scientific terms and imbuing them with quasi-religious meaning is not helping. In reality, people just eat stuff and make up stories they don't even verify to feel good with their choices. Which, like with other such belief systems, is fine, until they believe their own stories so much they try to force others to believe in them too.