This is a 'yes' and 'no' topic. When I take my car to be serviced I want the mechanic to be qualified. There are some backyarders who are good at this - but to the majority of people the mechanics apprenticeship and qualifications are important. When I want professional services, I want qualified people - doctors, lawyers etc to be working for me. Not someone's grandmother who is good at making chicken soup.
So if I want my children educated, in whatever topic, then at least Education qualifications demonstrate that the person has learned the theory, had some supervised practice, and has some understanding of developmental curricula, lesson planning, testing techniques as well as content.
A degree of any type should give the ability to read extensively and intensively, analyse and write, and so has some levels of preparation that are useful for teaching. But for professional teaching, pedagogy is important.
But along with the specific knowledge other skills are important. And for some professions people skills are vital. Enthusiasm and patience are important for teachers, a desire for your students to grow is necessary. And these things can't be taught, so we can say there are teachers out there with no quals who have these attributes and we can respect their accomplishments in the classroom.
But by saying this it doesn't mean that we should accept all native speakers without quals or 'off topic' quals as good either. If I really need a Dr., then I'll be happy with the one with the knowledge over the people skills If I'm not too sick - then the Dr who chats to me, is friendly etc is good enough. Same with teaching - if I really want to learn, then I want someone who actually KNOWS how to teach and why what will/won't work.