There are lots of different contexts, and for each I think there is a different answer. Advocates (not in the sense of a Barrister, but in the sense of supporting people to process information and communicate) are at pains not to advise or influence a person one way or another. Whereas a regular support worker might advise from time to time if that's what a service user wants. In cases where someone has impaired mental capacity (or perceived that way) people will feel freer to make decisions on their behalf, and the legal and ethical basis for this is very much a live issue in social care. It is almost universally accepted that very young children do not and should not have autonomy, and it is up to parents what leeway they allow their children. Exactly what role a friend should play in one's decision-making varies from friendship to friendship. Sometimes people want their friends (and/or family) to be heavily involved in their decision-making. Others regard the role of a friend to supportive but non-advisory, more like an advocate.

Article 8 of the ECHR concerns autonomy (among other things) and sets out some boundaries, although much of the detail of this is in case law I think. But it's good that the general approach is for public bodies not interfere in someone's decision-making unless it is necessary in pursuit of one of the legitimate purposes and that interference is done in a minimal and proportionate way.

General Comment 1 on the UNCRPD is well worth a read (it pertains to Article 12 of the UNCRPD). It sets out that best interest decision-making should never happen (if I remember correctly) even when someone is incapable of making their own decision. Their legal right to make their own decision is never lost, even if they are unable to exercise it. Where we cannot ascertain a person's will and preferences we basically guess what they are likely to be and act according to that, regardless of what we judge to be their best interests. I may have got that wrong but that's how I remember it.

Mental Capacity legislation varies from country to country and sets out how to support people to retain capacity and sets out the powers and duties around making decisions for others when they lack capacity to make those decisions for themselves.

In thinking about autonomy it is important to be clear about which decisions belong to which agent by default. For example, while a disabled person might rightfully expect very considerable choice and control about exactly how their support is delivered, the decision about whether they are eligible for support or not in the first place is not theirs to make, that is for the local authority to decide according to law, guidance and policy. Sometimes autonomy advocates are wrongly criticised based on this kind of mistake, saying something like "We can't allow too much autonomy or people will decide to award themselves absurdly large care packages," which completely misses the point.

Is it always wrong to interfere with autonomy or can it be right under certain conditions? — Tom1352

First, one would need to stipulate where, and in what form, autonomy resides. For instance, in deontological moral philosophy, autonomy can’t be interfered with at all, otherwise the concept is self-contradictory and the entire philosophy refutes itself.

Second, one would need to show interference is in fact an act upon autonomy, or merely an act upon the volitions that follow from it, or, nothing more than a hindrance with respect to personal happiness/well-being.

But to answer the question, from my point of view anyway.....interference with autonomy is impossible, so whether such interference is right or wrong, is unintelligible. Still, with a sufficiently broad notions of interference and autonomy, the possible connections between them become more apparent.

I would say, attempting to restrict someone whose actions are not restricting anyone else.

On the other hand, if someone's actions do negatively constrain a great number of other people, then constraining that person actually contributes to individual autonomy at the collective level. As when small groups of people co-opt public resources.

If you have to ask, whatever it is that you were planning on doing.

Is it always wrong to interfere with autonomy or can it be right under certain conditions? — Tom1352

I can think of a few scenarios. Essentially, when pursuit of prolonging or perhaps even expanding one's autonomy presents great risk toward one's anatomy! Of course, few who like to play king, queen, mommy, or daddy often care much beyond ensuring there are no new kids on the block. Not that they care about their survival really, simply put, "better the devil you know."