I don't have a source of him saying that's why he opposed return-free taxes. This article has links to the statements of his organization:

https://www.propublica.org/article/how-the-maker-of-turbotax...

His stated reasons are so fantastically stupid that I can't imagine them being legitimate. Return-free filing is the best tool we have to achieve his claimed goals of reducing the complexity and confusion of tax season. Can you think of an innocent explanation for his opposition?