I stand by my point, if you have to ask.. then it's obviously wrong.
It really doesn't matter if YOU wouldn't care, it's not your wedding is it?
Brides wear so many different wedding outfits nowadays, white/ with flowers/ lace/ short/ long/ train/ veil...
Is it that hard to pick up a different colour and not be that embarrassing guest?
It probably won't be that specific dress, but it's very easy to find a very similar-looking wedding dress.
I don't understand the rudeness of posters who show no regard for anyone else because everything has to be about them. It does explain some outfits you see ridiculed on social media I suppose.