What if, for example, the silence in question was for the death of the monarch or other royal, and you were vehemently anti-monarchy. Though you have respect on death for that person as you would any other human, you disagree completely with the exalted status and ceremony the death of this one person born into priveledge is commanding. It may be a belief that is rooted in religious history, or your beliefs on class and equality, whatever. Then, maybe, it is a big ask. What do you do?
I’d say most people would go to the purpose-built toilet cubicle, but I can imagine that there are some people that object to SOME silences so much they would wish to openly defy it.
But if someone feels that strongly then they could make a statement and defy it. But they might then have to deal with a bunch of people who perhaps equally strongly wanted to observe it. They would just need to weigh up how much it mattered to them. It's pretty impossible to live in any kind of functioning society without sometimes feeling that you have to do things that you might not do if left to your own devices.