Yea, the concept of burden of proof can be a useful social convention, but that's all it is. The thing is that taking a sceptical position and waiting for someone to proof you wrong is the opposite of what a sceptic should do. If you ever see two 'sceptics' both taking turns postinf 'you have the burden of proof', 'no you have the burden of proof!'... You'll see what i mean. Actual rationality isn't supposed to be easy.