First of all, most people who commit suicide are simply depressed.
Most of these people wouldn't want to die if they received appropriate treatment for their depression, including counseling and/or drugs. Empirically speaking, many if not most of the people who FAIL suicide attempts later feel glad that they failed and are grateful to be alive. (I know several such persons, personally).
Do you enjoy the "right" to commit suicide? Well, in fact, legally speaking, for years suicide was illegal in most of the United States. My understanding is that specific laws against suicide have been revoked in most states, so nowadays you can legally kill yourself, if you like. Assisted suicide is legal in a few states, though there are pretty strict rules regulating it. But just because its legal, doesn't make it "right". Suicide may seem like a good option to someone depressed, but its typically highly emotionally traumatic to the suicidee's friends and family.
With respect to the specific situation of someone who is at the end of their life, in many cases proper pain and mood medications can make the end quite tolerable. Unfortunately, these are often NOT administered correctly, and that's a shame. But yes, in certain cases, yes, suicide probably is a dignified alternative to prolonged suffering, and I don't have a problem with that.