Would it be fair to say that covenental marriage has been around a LOT longer than our legal system? To infer that marriage as a concept is somehow a political or legal institution is preposterous. Granted, civil ceremonies were introduced as a political/legal option because those who didn't prescribe to a faith-based religion still wanted an established and recognised covenant, the least benefit of which afforded them the same legal rights as those who were married.
To somehow infer that, therefore, the legal or political system 'owns' marriage simply isn't the case.
I'll grant you that the Church of England has knee-jerked badly over a lot of these issues, but I suspect that it was less of a 'control' issue and more to do with how they live out their faith and creeds amongst an ever-changing society. One thing I would ask though, is dont suppose that everyone who claims Christianity as their faith is somehow connected to the Church of England, because they're not. The CofE is very young compared to the Christian faith.
Cheers