Moral principles

Whether there is a moral distinction or not, largely depends on a particular society since it is the society that defines their moral principles. Morals are what the society believes to be right. There may be no distinction morally in taking the life of someone and giving him a means of taking his life. For instance, taking a life is considered wrong even upon their request by many religions. Also, it is morally wrong to offer someone the means of ending their life. It is just like shooting someone dead upon their request or offering them a gun when you are aware of what they are going to do with it. Death is final and an irreversible event hence giving someone the means to end his life is also morally wrong. In a nutshell, in the event your assist someone to end their life or give them the tools purposefully to do so; you are wrong by most moral or ethical standards.
However, there is a legal distinction between the two scenarios. The distinction is defensible ethically in certain circumstances. In some cases, it might not be wrong to offer someone a means to end their life. For instance, one may end his life by driving a car or drinking too much. Such scenarios do not make the seller of such tools complicit of the death. Also, in the event the act of ending someone’s life for them or giving them the means to do it is viewed as merciful, then it may be a good act since it is the mercy that is due to the other person. However, most moral principles that forbid taking someone’s life tend not to find any difference between a person performing the action and the person facilitating the activity.