Nah, they do need rules, and from my own experience, they are much happier when they know their boundaries...makes them feel secure, even though it's damned hard work for you
I got a bit pissed off with the media obsession with 'pester power' tbh. Every single generation has gone through it - it's nowt new. Kids will mither til their tongues fall off if you let them - it's up to parents to set the boundaries