Would you do me a favor and refer to this hypothesized agent as a DAI (Denis Artificial Intelligence)? Such an entity is nothing I would call Friendly, and, given the widespread disagreement on what is Friendly, I believe any rhetorical candidates should be referred to by other names. In the meantime:

Your other goals are immaterial and pointless to the outside world.

I reject this point. Let me give a concrete example.

Recently I have been playing a lot of Forza Motorsport 2 on the XBox 360. I have recently made some gaming buddies who are more experienced in the game than I am - both better at driving in the game and better at tuning cars in the game. (Like Magic: the Gathering, Forza 2 is explicitly played on both the preparation and performance levels, although tilted more towards the latter.) I admire the skills they have developed in creating and controlling their vehicles and, wishing to admire myself in a similar fashion, wish to develop my own skills to a similar degree.

What is the DAI response to this?

My point was that you used "you won't regret it" as a point in favor of wireheading, whereas it does not serve as a point in favor of death.

It seems you think paternalism is okay if it is pure in intent and flawless in execution.

You're twisting my words. I said that FAI paternalism would be different - which it would be, qualitatively and quantitatively. "Pure in intent and flawless in execution" are very fuzzy words, prone to being interpreted differently by different people, and only a very specific set of interpretations of those words would describe FAI.

It has been shown that vulnerability to smoking addiction is due to a certain gene. Suppose we could create a virus that would silently spread through the human population and fix this gene in everyone, willing or not. Suppose our intent is pure, and we know that this virus would operate flawlessly, only affecting this gene and having no other effects.

Would you be in favor of releasing this virus?

I'm with Alicorn on this one: If it can be made into a contagious virus, it can almost certainly be made into a non-contagious one, and that would be the ethical thing to do. However, if it can't be made into a non-contagious virus, I would personally not release it, and I'm going to refrain from predicting what a FAI would do in that case; part of the point of building a FAI is to be able to give those kinds of decisions to a mind that's able to make unbiased (or much less biased, if you prefer; there's a lot of room for improvement in any case) decisions that affect groups of people too large for humans to effectively model.

Your friend is depressed, and they want to commit suicide.

It doesn't follow that they prefer to commit suicide.

If this is leading in a direction where "wireheading" is identified with "being happy and living a fulfilled life", then we might as well head it off at the pass.

Being happy - being in a pleasurable state - isn't enough, we would insist that our future lives should also be meaningful (which I would argue is part of "fulfilled").

This isn't merely a subjective attribute, as is "happy" which could be satisfied by permanently blissing out. It has objective consequences; you can tell "meaningful" from the outside. Meaningful arrangements of matter are improbable but lawful, structured but hard to predict, and so on.

"Being totally happy all the time" is a state of mind, the full description of which would compress very well, just as the description of zillions of molecules of gas can be compressed to a handful of parameters. "Meaningful" corresponds to states of mind with more structure and order.

If we are to be somehow "fixed" we would want the "fix" to preserve or restore the property we have now, of being the type of creature who can (and in fact do) choose for themselves.

I can give you my general class of answers to this kind of problem: I will always attempt to the best of my ability to talk someone I care about out of doing something that will cause them to irretrievably cease to function as a person - a category which includes both suicide and wireheading. However, if in spite of my best persuasive efforts - which are likely to have a significant effect, if I'm actually friends with the person - they still want to go through with such a thing, I will support them in doing so.

The specific implementation of the first part in this case would be to try to talk them into trying the meds, with the (accurate) promise that I would be willing to help them suicide if they still wanted to do that after a certain number of months (dependent on how long the meds take to work).

I'm OK with the deletion of very-short-lived copies of myself if there are good reasons to do it. For example, supposing after cryonic suspension I'm revived with scanning and WBE. Unfortunately, unbeknownst to those reviving me, I have a phobia of the Michelin Man and the picture of him on the wall means I deal with the shock of my revival very badly. I'd want the revival team to just shut down, change the picture on the wall and try again.

I can also of course imagine lots of circumstances where deletion of copies would be much less morally justifiable.

Depends on how much it cost me to make it, and how much it costs to keep it around. I'm permanently busy, I'm sure I could use a couple of extra hands around the house ;)