Hegel derives the historic Enlightenment notion of Utility from a simple alternation of perspectives (being-in-itself, being-for-another, being-for-self) that is abstracted from all particular content. It is a sort of objective correlate for the “Pure Insight” that results from free use of the Understanding in practical matters.
The correlate of the Understanding’s freedom on the objective side is its abstraction from all content, which makes it “merely formal” in the sense we have seen Hegel criticize before. An alternation without content could go on without end, which makes it an instance of what he called “bad infinity”. Utility is “the awareness of the world as useful, not the comprehension of that world as the real self” (Harris, Hegel’s Ladder II, p. 380). It is the “pure self-estrangement of the Concept” (p. 386).
As with Understanding in general, Utility by no means appears only in a bad light. It is taken to presuppose a community of equal persons, and to imply the absolutely free Rousseauian general will of a sovereign People, which Hegel presents sympathetically. Consciousness is even said to “find its concept” in Utility (p. 384). Harris notes though that in Hegelian terms, the reference to “finding” indicates a less mature attitude than making or development.
A concept that generates a “bad infinity” ultimately cannot serve as a criterion for value judgment, because it leads to an infinite regress. But Hegel is not so much concerned with the theoretical error of the British Utilitarians’ reduction of all values to utility as with the political danger of the harshly “utilitarian” attitude of those who promulgated the Terror in the late stages of the French Revolution. The idea there was effectively that whatever action was deemed “useful” by the new authorities required no further justification. It seems clear to me, as it did to Hegel, that the French Revolution was a good thing on a historical level, but to acknowledge a generality like that is by no means necessarily to endorse every detail of the way it was carried out.
I have to say I think debates about whether or not “the end justifies the means” in general are pretty meaningless and unhelpful. We can meaningfully discuss the appropriateness of particular means to particular ends. The answer will be yes in some cases and no in others. Harsh measures that are unfortunately necessary in some cases are completely unjustifiable in others. Sometimes the tradeoffs can be very difficult. “Utility” as a putative criterion is only helpful in the easy cases. In difficult cases it ends up being tautological or sophistical. What is unequivocally wrong is the notion of arbitrary license, or the claim that no more substantive development of justification for an extreme course of action is even relevant in the first place.
Hegel is indeed concerned with a slippery slope here. The slippery slope concerns not the ends-means cliché but the use of utility as a criterion, which at the shallow end seems innocuous enough. But vague generality shades into arbitrariness, and utility is a vague generality. (My own judgment is that the notions of sovereignty and the general will are also tainted with what Hegel would call “bad infinity”.)