If by "chance" you mean real causes, then we are on the same page. The problem arises when we say probablistic. For example.. is it probablistic there was not an oxidizing atmosphere? is it probablistic some kind of proteins were in some organic soup? well one needs DNA for proteins. Maybe some Stanley Miller amino acids assembled into a primitive funtional protein. unlikely they all need to be "left-handed" is it probablistic DNA formed, well not without protein. ..is it probablistic some phospholipid bilayer assembled into a cell well (proteins and all) in order for the DNA not to be destoyed by the environment? I am not a biochemist so I do not know the answer to all these probablities but they are pretty high. Nevertheless may science march on to discover orgins I think it is fascinating.
The fact that life in this part of the universe uses left handed amino acids and right handed protiens is a matter of chance. In the evolution of life one form took hold and the other did not. There is no reason why life in some other part of the Universe would not be formed using chains which mirror our own. As a matter of fact there is an even probablity that life elsewhere in the universe would form from mirror image carbon chains. (If we were invaded by life made from mirror image carbon changes, we would not have to worry about them eating us. )