Maries I do wonder what would happen to statistics re CofE in the UK if, like here, being a member of said Church would incur a compulsory fairly hefty Church tax? Here people who would happily say they are Christian, in a cultural almost secular way- left in droves when said Church tax was made optional.
I actually totally agree with you that if gay couples want to marry - it is a secular matter, in a registry office- and that no Church, nor Vicar/Priest should have to marry them in Church. However, the problem comes when a Church, in this case CofE, is THE official Church, with all the privileges it entails - and therefore should abide by State Law. So a separation of State and Church, as in France or my own country, Switzerland, makes sense in the 21st C.