Both Math's and Dan Getz's answers are absolutely true, but deal with very different ideas that sometimes, under certain conditions, don't work well together.
It's true (as Math said) that there's never been a requirement to "show your credentials at the door" to any SE site, because it doesn't mae any sense to have one, and becaue it's actually detrimental to the site and its community. Turning people away from the site, or forbiding them from participating, based on not having the right qualifications doesn't encourage people to learn more and participate more. We cannot, and will never, do something like that.
On the other hand, the whole "ranking by committee" only works when the committee (the users) can be trusted to agree on a good, reasonable, effective answer (as pointed out by Dan Getz). If you have a huge group of beginners, their answers to the questions can't be truly trusted to be correct, no matter how much support it has from everyone else.
That's why you need a site that has experts, plural. So they can not only write good answers, but also figure out what is a good answer. Experts in a language are harder to come by than a good programmer, especially on the internet. It's comparatively easy to form a good group of great programmers (like SOpt has) than a big group of experts in the Portuguese Language, from Brazil, Portugal and other Portuguese-speaking countries.
That's where the community has to work the most, I think. The proposal had a lot of support from the SOpt community, which is great. But now's the time to reach outsite of it and recommend it to your Portuguese teachers/professors, your friends, and other people who'd be able to form a core community that's very distinct from the one that exists on SOpt.
It's not about making sure only PhD's can write the answers, it's about making sure there are enough people here who know what they're doing with their posts, and votes.