To me it's at least at much an equality, autonomy and access issue as anything else (though other aspects of the issue and other ways of looking at it are also important).
Suicide has been legal in England for over 60 years, and since whatever is not forbidden is allowed, killing yourself is one of the choices you're generally free to make for yourself (except when it's felt that your wish to kill yourself is the result of a mental illness, in which case you might be protected from yourself). The freedom to choose suicide may not be a freedom most of us appreciate, but it's an profound and important one.
When people want to exercise their freedom to make choices about things that are important to them, but are unable to do so without assistance because of a medical condition or disability, it's an access issue.
In the case of providing access to suicide, however, it brings up all the ethical, moral, legal and societal complications that people have been discussing. And I don't think that these are minor issues — implicating other people in the act of killing someone, the potential for coercion, the potential for policy creep, of course these are all really important and might be enough to mean we should keep the status quo.
But I don't think we should forget that underneath these issues lies a fundamental principle of equal access to important choices. If the ethical and societal difficulties are indeed so serious that we decide to continue denying people the assistance they would need if they wanted to act on their own choices about their own lives in a way that is legally permitted if you're capable of carrying it out unassisted, then we need to own that, and say that, to prevent other potential harms, we are choosing to restrict the freedom of some of the most vulnerable people to make choices that other people are allowed to make.