Found a source for this opinion. Here [1] are instructions from the Dutch Government's "Personal Data Authority" on setting up GA in compliance with their laws in a way that does (did?) not require an explicit notice. See [2] for an explanation in english
Opt-in via an explicit dialog, and, most importantly, you have to give the user the ability to select "no" and still use your website (in which case you aren’t allowed to do any tracking).