I have recently signed up in a new casino and I'm receiving some bonuses with the wagering requirements we are discussing in this thread. The thing is that I have always thought that very high wagering requirements are abusive, but taking into account that the bonuses I'm receiving aren't linked to any deposit I make, I suppose that it is fair for that "free money" to be used as "test coins" and only be able to withdraw for real money after a very lucky strike. In the meantime, the player gets fun and used to the casino at the same time.
Of course, these bonuses are meant to be the hook for many gamblers, but I don't think this is the same case as other bonuses that depend on the deposited amount of money or, of course, abusive wagering requirements for not bonuses but simple deposits.