I would say look on it as a dress with experience

It knows how to perform and make you look wonderful because it's done it before. OK so now you think I'm mental, but these dresses have a history and are so beautiful they should be worn and worn again by many beautiful brides all celebrating their special days. I think it's so sad for wedding dresses to be shut in a wardrobe to gather dust when they could be enjoyed by someone else.
And you're right, this dress has only been worn by one other person, whereas a sample one would have been worn by many, pinned a good few times etc.
If this is the dress you love, go for it. When you've got it on and it's yours and had any alterations done, you won't feel that it's second hand, it will just be the dress of your dreams.
Besides, recycling is very good for the planet and if you were wearing vintage dress you wouldn't worry about the original bride, you'd think, wow a dress with history - that's all a second hand dress is! And I agree, in the case of a wedding dress, second hand means somebody else has worn it once for a few hours, I don't think you'd feel bad and I don't think there should be a stigma about pre-worn wedding dresses. Good luck finding your dream dress x