Myth #1: Everyone can do testing
IMHO: Yes, I agree. Everyone can test the software just like everyone can do the cooking. But some food you will eat just one time… Good testers can save your business, so this is up to you, how high risk you want to take.
Myth #2: Test cases are the only way how I can measure software quality
IMHO: Test cases do not measure or assure quality of the software. Test cases are something like collection of instructions how you want to test the software.
A good tester can test the software without any written traditional test case. Software can have bad quality despite tousends of test cases.