They have the right to stop production on all cards that look exactly like or are made to look as close as possible to their product. That's not monopolizing all product parodies.
How is a competing product NOT going to 'look like theirs'? Wackys are made to look like the product that they are spoofing. A competing parody would likewise look like the product they are spoofing. So, the competing parody would look like a Wacky? No, it would look like the product that it was spoofing.
These days, there is nothing that sets a Wacky apart.... nothing that 'makes it a Wacky'. Historically, you could argue the thick black border, but, anymore, they are simply parodies (and not always of products!). Colored borders? Sorry, Topps doesn't have a patent on color. Nobody owns red or yellow or silver or etc.
Not monopolizing all product parodies? It certainly is an attempt to, and I'm pretty sure everybody knows it. It's the same strongarm methods that Microsoft used when they tried to run Netscape out of the browser business. All because they couldn't handle a little competition (actually, Netscape was kicking their ass). Topps wants this same kind of domination.
In the Microsoft situation, Netscape initially gave them the middle finger because they had their own income and didn't rely on Microsoft for any of it. In this case, Topps literally holds all the cards. Topps is where your bread is buttered, and they know it. It's not like you can walk across the street and make the same money for some other parody card company. Because there is no competition, Topps doesn't have to sue you, or even threaten it. They'll just blackball you: Go ahead, make your little Halloween set... you'll never work for us again! You're stuck, they've got you, and there's nothing you're going to do about it. Oh, you could go to court with them (and even win, like Netscape did), but, you'll drown in all your legal bills. You'll be bankrupt, blackballed, and unemployable, but they'll still be producing WP and GPKs. What will you have gained? Nothing. It's a shitty business practice that's been around since the dawn of time.
Please don't take any of this as an indicment on the artists. Y'all gotta eat and pay bills. If you have to cancel a Halloween set to keep yourself employed, so be it. And, I don't blame you one bit because I would do the same thing.
Sure does cast a dark shadow over this weekend for me, though.