Purpose of a blog

I think the purpose of a blog is that people who live for away from each other can keep in touch and have a way of communicating with out it costing alot of money. the pros that i see are that once agian that people can communicate over long distances and it not cost alot of money, cons are that some people put bad things on other peoples sites or there own and that any body can have or get access to your site unless it is something like this. some are safe and some are not safe like myspace and facebook where people put sick things on there sites and lie about there age and other things. They can be used as an educational toolfor many reasons kike your theacher can put assiments on them like blackboard and its a way the parents and students can communicate with the teachers.