I think that as long as Apple stays impartial, verifies the identities of developers, and fights attempts by governments to abuse revocation, this is actually a development we should welcome and encourage.
Imagine if by default, all software most users install on their Macs will be traceable to a real entity - be it a person or company. This entity can be held responsible for the behavior of the software it distributes. If the distributed software is malicious, it's possible to immediately revoke the entity's certificate, stopping the software from running on future, and possibly even current machines. Legitimate entities that don't distribute malware are only mildly inconvenienced whenever they register or renew their Mac Developer Program membership.
In fact, a system like this only has value if it's difficult to opt-out. For an example of how useless signing is without a mandate, look at Windows: Unsigned apps run just fine, and most malware has no certificate to revoke - it keeps working long after it's discovered.
Even better, if all applications are required to be signed, it's now possible to verify the signature of everything on the system. You can prove that nothing has been tampered with, and in the event tampering has occurred, you potentially know what to replace to return to a known good state. I think this alone is awesome!
Now, could Apple use this to stifle competition? Maybe. Does it raise the bar to distribute an app on the Mac? Sure (but I'm not sure that's a bad thing). As long as disabling the signature mandate is an option, power users are free to do whatever they want, and most other users will be much better off.
The problem is with the hypothesis that Apple would stay impartial and fight attempts by government to abuse revocation. This is highly unrealistic, and we've already seen Apple use the App Store policies to keep competitors' apps out (Google voice for a long time, 3rd party browsers, ...), calling them "redundant functionality".
I think that even if you add up all of Apple's indiscretions so far (and I agree with you they've made mistakes), you'd find the number to be small, and the number still outstanding even smaller. It's not going to be a perfectly smooth ride, but as long as disabling signature verification is an option users will be able to work around Apple's obtuseness in situations like this until they're resolved.
Imagine if by default, all software most users install on their Macs will be traceable to a real entity - be it a person or company. This entity can be held responsible for the behavior of the software it distributes. If the distributed software is malicious, it's possible to immediately revoke the entity's certificate, stopping the software from running on future, and possibly even current machines. Legitimate entities that don't distribute malware are only mildly inconvenienced whenever they register or renew their Mac Developer Program membership.
In fact, a system like this only has value if it's difficult to opt-out. For an example of how useless signing is without a mandate, look at Windows: Unsigned apps run just fine, and most malware has no certificate to revoke - it keeps working long after it's discovered.
Even better, if all applications are required to be signed, it's now possible to verify the signature of everything on the system. You can prove that nothing has been tampered with, and in the event tampering has occurred, you potentially know what to replace to return to a known good state. I think this alone is awesome!
Now, could Apple use this to stifle competition? Maybe. Does it raise the bar to distribute an app on the Mac? Sure (but I'm not sure that's a bad thing). As long as disabling the signature mandate is an option, power users are free to do whatever they want, and most other users will be much better off.