Being a high profile actor can be a tough job. It's an extremely competitive field, so there's always this innate desire to placate and appease people, especially directors and producers.
On the other hand, actors and actresses who don't take chances and stick up for their work rarely get noticed. Cause too much of a fuss or rock the boat too much early on and that could mean curtains for your career.
But once you establish a bit of a name for yourself and earn a reputation in the business, I'd imagine that being vocal about what you like or don't like in a film you're working in becomes easier. It's still obviously terrifying because these are multi-million dollar budgets we're talking about, after all, but if some famous actors didn't take huge risks or make their opinion known, we probably wouldn't care about them as much as we do.