By default LO shows the following formatting marks ( Tools > Options > LibreOffice Writer > Formatting Aids > Display of )
* Paragraph end
* Soft hyphens
* Non-breaking spaces
* Hidden text
I think that non-breaking spaces and soft hyphens should be hidden and hidden text should be shown. The display of non-breaking characters and soft hyphens as gray highlights causes more harm than benefit in its current broken state (bug 58434) and without hidden text enabled, hidden text would never be visible to users until they first new to enable this in the options dialog.
Would agree if bug 58434 gets resolved. Otherwise the current defaults work--really is no need to show hidden text by default, advanced users likely to use it will know to set it enabled.
Since reported already confirmed his own bug (which is not favorable), I can't but support this.
With Hidden text checked in Formatting Aids, it's still not shown, unless we use NpC (just created acronym that stands from Non-printing Characters).
MSO also works like that, NpC turns all on, and that you can change (in 3 clicks, while LO options take 5)
Primary concern should be non-advanced users, which would hardly figure all this out. So, it's easier to have it checked and let those advanced to uncheck this.
Please add keyword 'needsUXEval' and CC 'firstname.lastname@example.org' if input from UX is needed.