I understand that, but I think returning them is actually more likely to help others than hurt. HD has pallets more of the bags, likely from the same lot, so people are going to get them whether your 4 bags go back there or not. And in many cases returned merchandise doesn't go on the shelf; it goes back to the manufacturer. And more importantly, if you ask for a manager to take a look, no guarantee but there's at least some chance they'll take action on the whole lot. They might be willing to open one of them and see. HD has a lot more buying power than you do, so if they do have multiple reports of defective product there's a better chance of them getting Morton's attention.
And in the end, you bought a product from them that you aren't happy with because it isn't as advertised, and per their policies are entitled to refund the unused products. I'd even bring in the empty bags with the pictures, as they might even be willing to refund all of them. But in any case, if I were running a store I would want to know if there were real problems with any of the products I sold so I could at least track them.
Do you have pictures of the salt in an opened bag, and pictures of the lot/plant info? That would be a great data point to compare. I'm going to stick with the Diamond Crystals brand, but it is good for people to know what to look for or not.