It's not used to validate transactions; it's used to protect the transaction from double-spending, i.e. to protect the property from theft. It's impossible to

It's not used to validate transactions; it's used to protect the transaction from double-spending, i.e. to protect the property from theft. It's impossible to protect private property without a cost. Usually, private property is protected with laws and guns, but not everyone has access to these, or they come bundled with various external costs, or they fail to provide protection. Which is why Bitcoin is useful.