I think it depends whether player 2 actually knows the refutation and how convincing the refutation is. You're going to have to give more specific examples of each case. Certainly the Whole KG seems a bit dubious at super GM level but even comes out from time to time. Some refuted sideline of it like the Salvio Gambit or something can still be messy at club level but if Black knows the line White will be suffering. Even the Muzio has taken some scalps at the GM level but in those games Black chose not to play one of the widely known refutations for some reason or another. In both of those cases I wouldn't like to play White against a prepared player whatever their rating. I don't play the other lines and can't speak to them. I guess I'm speaking to sidelines that actually are refuted, but I think that's what you're talking about? If you're talking about sidelines that players think they can refute over the board based on something a higher rated player has said but which actually are fine, then I guess I agree with you, but I don't think that actually happens very often.
"Refuted" Openings
I was talking about an uncommon opening that works fine at non titled player level, and fits specific styles. Many GM coaches have these openings are great for specific styles of players. For instance, a player who relishes wild positions with pieces flying would probably prefer to play the king's gambit over a ruy lopez, even though the ruy lopez is a "better" opening. In my opinion, even sidelines that are actually refuted can be fine for certain players, but I wasn't talking about those lines.
Thank you for the clarification.
I recently bought a german book on 1...d6 against nearly everything. The repertoire is designed for students with around 1400 - 2200. The Authors (IM Zude and GM Hickl) say, that white has a small theoretical plus in some lines, but the theory changes not that fast there and you can still count on your greater experience, while your opponent is likely not familar with the positions.
Before that i tried to study 1...e5 and 1...e6 mainlines with much much more theory. For a week or so i even tried the caro-kann, but that's still much more theory then i would like to study.
Yes, the englund gambit, borg gambit and so on are refuted. But i have not that great score against them in blitz and bullet chess.
Looking around the openings forum, I've noticed a common pattern in the conversations about "sideline openings":
Player #1 says, "Can you please give me some advice on this sideline opening that I like the look of?"
This could be a variation of the Modern defense, Dutch, King's Gambit, Evan's gambit, etc.
Then, Player #2 says something along the lines of, "This opening really isn't that great. I can certainly refute it!
This player is usually not titled and, in some cases, lower rated than Player #1. This is not only completely incorrect, as these openings are only considered to be slightly "dubious" at super GM level, but it is comically arrogant, because all that Player #2 has probably done is relayed the information from a player with nearly twice the rating as them.
Does anybody know why these people are so focused on demolishing somebody's plans about an opening which fits their style of play? I personally see no problem with these openings for non titled players.