It's a central tenet of debate that if you hold a strong view, strong enough to make a big criticism of a person or organisation, you'll probably be asked to explain it.
If in response you refuse to explain why you hold a view, or even suggest it's wrong for someone to question your view, and go on to accuse the person asking of trying to remove your right to an opinion, or try to change the subject, it's likely to lead people to the conclusion that your original claim is based on your own bias rather than on the facts.
Indeed, if the people involved had perhaps spent more time trying to use these principles, and put more effort into understanding the position of TfL and LU management in regards to what TOCs would ideally like, we might by now have a negotiated agreement between parties on a way forward, rather than people just having a go at them.