But a utilitarian has no reason to see them as being immoral.

That’s the crux of the issue. A hard-core utilitarian has already decided that coercion is a legitimate tool to fix various perceived problems. What he fails to realize, though, is the inconsistency of his position: that coercion is fine as long as long as a desired end is achieved, but he will cry foul when he is the one being coerced to satisfy a different conception of morality than his. For instance, when the Taliban uses coercion to enforce “piety”, the leftist utilitarian suddenly discovers that it actually is immoral to use force (or the threat of force) to institutionalize a narrow strain of morality. This works for the right-wing religious zealot as well.

While true believers may be all but a lost cause, one hopes that average, middle-of-the-road folks who are naturally predisposed to either “social justice” or “tradition moral values” can eventually be persuaded by the value of logical consistency.

Giving leftists the benefit of the doubt … it seems that their ultimate goal really is “the greatest happiness to the greatest number”; but the means that they prefer not only have failed—and are failing—miserably, those means (coercion, confiscatory taxation, etc.) are intrinsically immoral.

This is what I was talking about in regards to utilitarianism the other day. To a utilitarian leftist, coercion and confiscatory taxation are not immoral if they achieve the ultimate goal, being the greatest good to the greatest number.

You’re entirely right that these methods don’t work, and won’t work, given human behavior and the incentives these methods create. But a utilitarian has no reason to see them as being immoral.