Nobody has said that ALL were. But it is like the old addage of taking an exam That any question that use words like "All" and "Never" are usually false because there are always exceptions to the rule that very few things in life are absolute including the popular conceptions of the institution of slavery in the south in 1860.
Contrary to that popular conception is the fact that at least some southern slave owners had excellant relationships with their slaves, as well as Free blacks in the communities. When you are talking about 4,000,000 blacks in the southern states and given the number of references that David U. and others have provided and the, in my estimation, 1% figure of 40,000 blacks in confederate service is not unreasonable to me.
Did these blacks carry guns? Obviously some did. It is hard for me to understand that if a man was carring a gun he was not a soldier. Whether he is only a muster roll or not. But no matter, a blacksmith was a skill that was very important to keeping a Cavalry regiment of an Artillery battery effective in the field. For every black that was in service in this manner it kept a white man in the line holding a musket.