One solution in that case is to
1. Let them have their way.
2. Create a paper trail so they can’t blame you when they discover that they were wrong. This will also provide them with a face-saving out, so they don’t torpedo the project. They will, of course, take credit for you ideas, or minimize your role in offering them.
Working as an R&D engineer in the aerospace industry I had several experiences with proposing off the wall solutions to problems. Higher ups would let me go but I knew failure was all mine. However, the company I worked for and the higher ups were all honorable persons who acknowledged success without claiming personal glory. A good bunch of people and company to work for.