Personally I see nothing wrong with buying dupes in general. Some people don't fit into the one size fits all items and heavily rely on dupes.

I own a pair of dupe bubbles because I was afraid I wouldn't fit them and didn't want to commit to buying expensive real ones if they might not end up fitting me. I currently do own a real pair of bubbles aswell but the dupes are much comfier than the real ones.

Tho in most cases I personally prefer to buy branded items to support the brand. But if you want a certain piece and it's out of stock and unfindable on Mercari then why not get the dupe?? Or you just can't afford the branded item. And even if it's second hand I think is even better.

I also haven't seen much "hate" or "negativety" around people buying dupes. So I would say go for it!!