Economically putting up barriers for the sake of it (aside from valid issues of qualification required for the public good) is bad policy. It's good for the people who can get the qualification, but bad for everyone else. When you average it out, it's worse for society as a whole (this is roughly implied by the Welfare Theorem's of economics).
Your argument that other professions do it is invalid. In fact the government should be more proactive in ensuring that professions only impose valid conditions on employment, and don't add spurious requirements in order to exclude people from the profession, in order to, as you say "protect [their] careers and incomes".
Your argument that other professions do it is invalid. In fact the government should be more proactive in ensuring that professions only impose valid conditions on employment, and don't add spurious requirements in order to exclude people from the profession, in order to, as you say "protect [their] careers and incomes".