Some critiques offered by Wizardry and Steamworks.
One of the immediate questions that arise from Bakunin's critique of the social contract, is that Bakunin actually does not criticize the social contracts itself, in terms of explaining why the exchange of power, or the separation of responsibilities, between the state and individual will not work. Instead, Bakunin illustrates that there are edge or mariginalized cases that might fall out of the social contract and, as such, the mariginalized cases, as large as they might be, will be excluded from the benefits of a mutually beneficial agreement.
However, looking back at utilitarianism, it stands clear that societies find themselves in a perpetual adjustment to maximize the happiness of the largest number. Perhaps, the process though which such adjustments are made are through revolutionaries like Bakunin that find themselves in a good position to illustrate that the Paretto-curve of utilitarianism has been neglecting certain people and that it is time for an adjustment. Then again, it is questionable whether such a degree of cynicism is a result of historical realities or rather fundamental realities, ie: Jeremy Bentham has been writing his works about a century before Bakunin and his theory would not allow by definition such inequalities.
Historically speaking, utilitarianism has overall allowed for progress and even the most draconic empires have ultimately come to reason and have made adjustments in the utilitarian sense; whether that is general liberty of individuals, freedom of speech, sexuality, etc. Nevertheless, like all cynics, Bakunin's observations on realities stand and should be granted as much of a benefit of a doubt as it has been granted to Adam Smith's invsible hand. Furthermore, other philosophers opposing the state, such as Robert Nozick have tried to reduce the size of the state instead of asking for a complete obliteration. Quite on the contrary, Nozick's restriction on the minimal state would require a very reductionist and almost counter-intuitive way of thinking in order to somehow deduce that a minimal state would (also) lead, as Bakunin would dogmatically imply, invariably to slavery.