Companies should be able to use rejected products (within food safety limits) but in my opinion they should advertise that that is what they are doing. Companies that do this should also charge less for products like this and not pretend that they are superior to products that do not contain rejected filler. Using crushed products in this way does reduce waste and in theory should reduce price for customers.
It makes perfect sense to use rejected candy bars as fillers. There is nothing wrong with these candies from a food safety standpoint. They are using the ones that have broken or unacceptable for packaging. It would be wasteful to throw these candy bars away. It is also cost effective to re-purpose rejected candy bars.
If the rejected products are just because they are cosmetically defective, then why not reuse them? What is it going to hurt? It sure is better than just throwing them away and wasting the money. This is a great way to reuse and save money, which could help save the consumer money in the long run.
As a consumer, you have the right to purchase or refuse any product you want; no one is forcing anyone to make buy any one product. While some consumers may object to the practice, if using the crushed bars results in the same product as the past, the brand is not even under moral obligation to notify consumers.