I think you are looking at it all wrong. I think for some (like myself) wearing a cross is a reminder to myself of what I believe. It is not a crutch but it does help people remember that God is with us all the time. It is not boastful, it is mindful. If something like an icon or a crucifix helps you be a better person then by all means wear one and if you don’t need it, don’t wear one. Not everyone is as strong as you are and need something to remind them and help them feel safe and protected. It is a personal choice and an exercise in religious freedom and should remain as such.
That’s a fair enough argument, but I dont think that is what Rowan Williams is getting at. There are people who think that a cross is just a nice bit of jewellery. There are people who think that “going through the motions” of Christian ritual, including wearing a cross, somehow make you a Christian. There are people who, even subconsciously, make the symbol more important than what it represents. And that nominalism is what he is criticising. And rightly so too.