Why do they need to look at it? The only reason this mechanic exists in the first place is to prevent multiple Sea Hags putting multiple Curses on top. Ergo, to change the card as little as possible while preventing good cards from being skipped, the Curse left by a previous Sea Hag is the only thing that should be discarded. I see two and a half ways to do that:
1a) Each other player reveals the top card of their deck, if it's a Curse, they discard it.
1b) Each other player looks at the top card of their deck, if it's a Curse, they discard it.
2) Each other player may discard the top card of their deck (without looking at it).
#1 doesn't require everyone to make a decision, but gives information about next turns, in a different way to how Actual Sea Hag does. If Actual Sea Hag reveals a Sea Hag, you know you aren't getting a Curse next turn, whereas if Nerfed Sea Hag reveals one, you know you are getting one. OK, that's not so different as to change how the card is played in most situations; there are edge cases where you know the Curses will be empty before you can play a Sea Hag you could leave on your deck with Scheme/&c, or more commonly, knowing how many Curses are left helps you decide whether to buy a second Sea Hag. But the information about what card is coming up could affect how I play my next turn (e.g. I left a Silver on top, so it's better to play Steward for Cards than for Coins; I left a Sea Hag on top so I'd better not play it for Cards), which I think is a substantial difference. It also makes Wishing Well really good.
#2 is the minimal change, you will discard if you already saw your Sea Hag, or you know it's a Curse because somebody else played Sea Hag. It seems to change very little about how the card would be played, and also seems nicer to me for aesthetic reasons.