The only requirement for joining the Guild is wanting to. The purpose is to discuss homeschooling, unschooling, or related forms of education, but Guild members are welcome to discuss anything that want (provided it doesn't break any rules).

By the way, just so that you avoid unnecessary stress I thought I'd let you know that you don't have to worry too much about what you say in your join request. It'd be nice if you'd give a little information - you are homeschooled, you're thinking of homeschooling your kids, or whatever - but you don't have to come up with an advanced description of your reasons because really if you want to join the Guild I think that's a good enough indication that you have sufficient reasons.