This is a semi-comment/semi-review article really, but the point I make I feel is rather important.
Their Morals and Ours is an effective exposition of the class basis of morality. In it Trotsky attacks socialists and other lefts who claim to adhere to a universal morality, exposing that anything that is supposed to remain constant for all time can only emanate from some sort of ‘god’. Marxists on the other hand have a dialectical understanding of society, noting that society changes and that all ideas (including Marxism) are interlinked with the material conditions in a given stage of society.
But it is the discussion of ‘means and ends’ that I found the most interesting. Here Trotsky discusses the famous statement that ‘the ends justify the means’. He explains that for Marxists that these are interdependent, that only the means that genuinely serve the ends of the liberation of humanity from capitalism are justified. Thus they must unite the working class, strengthen its party (both internally and externally) etc. Thus such things as individual terrorism fail such a test as they tend to weaken the working class and divide it rather than strengthen it.
The context of such actions is also important. It is one thing to shoot someone in the street in cold blood, it is a different thing when one is on the front line of a war. Thus the same action can be justified or not depending on the context. The relevance of such a recognition is very useful for developing a Marxist critique of criminology.