That's a very simplistic and, I think inaccurate view of the matter.
My customers, for example, to whom I provide service, are not infringed upon in any way because I use private forks of GPL software in the provision of my services.
My customers, for example, to whom I provide service, are not infringed upon in any way because I use private forks of GPL software in the provision of my services.
The issue is that I—and, more importantly, your customers—must simply take your word for it, since we're unable to confirm or deny it for ourselves if you don't make the source available.
When dealing with large corporations, taking such statements at face value is pretty foolish.
You might not want to admit to yourself that your business model is based on infringing on the freedoms of these users of GPL software, but that's exactly what it is.