Characterize snowball as a leader in Animal Farm. Do you think his reaction to the stable-boys death is the appropriate reaction to have during a revolution?

During the Animalist uprising, the big old shire horse Boxer accidentally kills a stable-boy. Boxer feels somewhat guilty about this, but Snowball tells him not fret over it as the only good human is a dead human. This incident, and Snowball's reaction to it, shows us his ruthless side. Like the fanatical ideologue he is, Snowball believes that the end justifies the means. If some individuals get hurt or even killed in the course of a revolution, then that's just too bad. So long as the revolution is successfully carried out, that's all that matters.
Snowball is supposed to represent Leon Trotsky, one of the leaders of the Russian Revolution. Like Snowball, he too believed that the end justified the means. Though often presented as a more moderate figure than his co-revolutionists Lenin and Stalin, Trotsky was in a actual fact no less ruthless, and was every bit as prepared to countenance death, violence, and bloodshed as a means of attaining and consolidating Bolshevik power.
As to the appropriateness of Snowball's seemingly callous actions, there are two ways of looking at the question. From a moral standpoint, his remarks to Boxer are completely unacceptable. There is simply no justification whatsoever for the taking of an innocent life, be it human or animal.
From a revolutionary standpoint, however, Snowball and others like him would argue that such deaths are a necessary, unavoidable part of any violent uprising, and are in any case a small price to pay for the ultimate victory of the revolution. Which standpoint we choose to adopt depends largely on whether or not we are political revolutionaries.