@tpr I am not saying Grand Prix is bad, I play it myself. I am just saying that I think against good black play this is as good as it gets for white. And if black goes d5 on move 1 it's not so easy to get that e4 move in that you would need (though often it is possible with d3 Nd2 first).
Playing Grand Prix with black is very sensible IMO since one tempo doesn't make that big of a difference in that opening so blacks opening disadvantage isn't too big.
And yes, white has to suffer a bit in that gambit, but objectively black doesn't have enough compensation. But if you know your opponent doesn't like defending you can try of course. (but at least I never was afraid of defending passive positions if I thought it was objectively good)
EDIT: Defending correctly becomes more difficult with shorter time control (as you might not have the time to figure out the best defense) so in online games which usually are blitz I do agree that it's very playable. But I wouldn't recommend it in long games.