They will argue that by providing a coupon that lowered the price for the customer they did in fact facilitate the sale. IANAL but this sounds reasonable to me. Less so for the sales they did not find a coupon for (even if they argue they've tried).

The rest of your comment folds under this.

I guess we'll see how this plays out, but for what it's worth, the attached filing does not argue "cookie stuffing". (It argues other things.)

This may also go to a completely different direction of e.g. "securities fraud" -- the SEC may argue that PayPal, as a public company, has advertised their Honey service as "finding the best deals for their customers", and on the basis of that claim some of the investors chose to buy its shares. If this was a lie, the shares sale was made under false premises, and that seems like "securities fraud".