You should check out what's needed to protect yourself legally, and see what the going rate is to have an expert help you with that sort of thing before you start saying stuff like "suppressing independent thought".
That's what I think.
Yes all game designers and authors of any material to be published should be aware of and comply with copyright laws but what this attorney is doing is scare advertising in my opinion and hurts the independent game designers and suppresses creativity.
Some commercial games allow addons and fan games because it helps promote their games.
The big issue is with knock off games using ripped sprites and using a well known registered copyright and trademark in the title and you will find black market copies of Nintendo games all over usually produced in foreign countries and they do take that serious.
I just think the article is way over the top scare advertising and needs additional clarification as to what you can and can not do legally. Parody and using sprites in public domain or unique homemade sprites that RESEMBLE but are not copies of commercial sprites is legal and there are also fair use laws that apply.
If you want to create a unique plumber character that jumps through unique plumbing and kicks unique turtles and you make it clear it is parody it is extremely unlikely you would face any legal challenge but companies will try to scare you off and if you do receive a DMCA notice take your game down but ask for the exact sprites or assets they claim are being infringed and for the exact game or source of the infringement.
If they can't give you an exact source it is just a scare tactic. Make some changes and avoid close resemblance to a commercial game.