I am glad that you "don't care" about breaking a few million phone systems across the world. Every single IT manager, however, does care. If you start having carriers wholesale-blocking calls based on their lack of STIR/SHAKEN's verifications, then you will completely disable the vast majority of IP- and POTS-based phone systems in the country, many of which were purchased/installed in the early-2000's.
You can have the "I don't care" attitude when you have one telephone number in your life. You have to care when you have a couple hundred thousand telephone numbers in your life, like I do, working for a Class 3 ITSP.
