"...he is implementing the democratic will of the majority, that is a higher authority in my opinion."
It may be your opinion but it's still wrong. Parliament is the supreme authority in the UK, and has been since essentially the 17th Century. While it was correct for Parliament to vote through Article 50 legislation that doesn't mean that they were obliged to (constitutionally, at least, although for sure morally there was little option).
Now it seems that David Davis et al are determined to respect Parliamentary sovereignty only as a sort of "rubber stamp" for his, and the cabinet's, position. That's not tenable, and it will come back to bite them.
The defence of die-hard Brexiters seems to be that it's impossible for any scrutiny to be applied by anyone without ruining our negotiating position. I'm happy to accept that I, personally, have no right to see what's going on behind the scenes in order to scrutinise the government's plans. Quite apart from anything else, what meaningful scrutiny could I give it anyway? But the Select Committee of Parliament, and by extension Parliament itself, has a right and a duty to understand the plans and process, and guide them and comment on them as necessary. By denying key information that denies Parliament the role it's entitled to play.
There's a further point, and one that I am sure May is trying to ignore in particular. The referendum is not the only way for the public to express their views on how the country should be run, and by whom. That's what general elections are for. Theresa May, David Davis et al, applied to the country for a mandate to implement Brexit in the way they saw fit. They did not get that mandate. Carrying on regardless is contemptuous of democracy as a whole.
OK. So clearly I have a self-interest in seeing Brexit scrutinised by, among others, the well-known not-Brexit-supporters Keir Starmer and Hilary Benn. So let someone who supports Brexit speak for me instead:
https://www.express.co.uk/news/politics/885224/Brexit-news-Jacob-Rees-Mogg-Brexit-impact-papers-David-Davis