The main reason why pasteurization sucks is because it causes juice to taste foul. And the most potent pasteurized green juices taste even worse than pasteurized fruit juices because those green juices have less sweetness to mask the bad taste.
Pasteurization is a preserving process used to dramatically increase shelf life in items sold in supermarkets and other retail outlets. The process was created to make certain products (usually of low standardization) created using specific manufacturing methods such that those products could be delivered long distances away and kept salable and consumable for very long periods of time.
High-pressure pasteurization (HPP) is more commonly used for juice than heat pasteurization is, but the results of both are about the same. Milk and pasta are heat pasteurized, and almond milk and oat milk are usually pressure pasteurized. Whichever pasteurization process is used for a given product, though, the result is that the product is not fresh.
Another reason to be concerned about pasteurization is that it denatures or alters enzymes that are otherwise beneficial to a person’s digestive system. It adversely affects the micronutrients in juices, so pasteurized items don’t strengthen a person’s body chemistry in the same way that fresh products do.
For those reasons I’m totally opposed to the pasteurization of products. Juices should be served and sold raw and unadulterated with no preservatives or additives so that their nutrients will be of optimal benefit to consumers.