I'll admit, I don't like strapless. I would never condemn someone for wearing a strapless gown, it's just not a look I like for myself - strictly a matter of personal taste.
But I do have to wonder what Miss Manners would have thought of my Renaissance costume wedding...I got married in shades of green, for one thing (I don't, in my own opinion, look good in white - as a pale-skinned blonde, I think it makes me look even paler, and not in an elegant way). And Renaissance brides didn't necessarily wear white, they wore whatever their best dress was at the time.
Anyway, I wonder if Miss Manners just isn't making sufficient allowance for the dominance of strapless in wedding fashion over the last decade or so, to the point where for awhile it was hard to find anything that wasn't strapless. Not everyone can afford to customize a dress or to have one made, so if strapless was all that was available, I'm sure a lot of brides who would have preferred otherwise ended up in strapless gowns anyway.
Edited to add that I kind of hope that the wedding of the Duke and Duchess of Cambridge will help to end the overwhelming dominance of strapless gowns. I thought she looked lovely, and very classy. I don't see anything "wrong" with strapless gowns per se, I'm just a fan of there being more choices than just strapless.