I think the idea of what is natural, and what unnatural, in ethics stems from beliefs about the proper or normal development of a human being. Such beliefs need a context. Aristotle, for instance, in his 'Politics' and 'Nicomachean Ethics', plainly thinks of a human being as having an inbuilt developmental pattern such that he or she can flourish - enjoy objective well-being - only if a range of virtues or dispositions are possessed and exercised. These are the ethike aretai and the noetikai aretai : moral traits such as courage, justice, self-control, and intellectual traits such as phronesis or practical wisdom.
It's important to see that Aristotle regarded a life in which the moral and intellectual virtues were possessed and exercised as the right, the proper, the 'natural' life for a human being, just as natural as an acorn growing into an oak tree. All sorts of assumptions sit behind this view but mainly the idea of there being an authentic pattern of life which, as a matter of fact, human beings have an inbuilt tendency or drive towards and without achieving which they objectively cannot flourish. One of Aristotle's views was that the proper life for a human being involved participation in the self-government of the polis or city-state. He really believed this; political life is 'natural' to a human being, an essential element in a flourishing life : hence his famous phrase that we are 'political animals'. So Aristotle can tell us quite clearly what is unnatural - for one thing, it is life without political participation.
A similar view of proper or normal development can be traced in Christianity. A philosopher such as St Thomas Aquinas will tell you that you were born to live in a certain way : to have faith, to worship God, to act charitably towards your neighbour, to forgive offences against yourself, to avoid pride, to see the present world as only a prelude to the perfection of heaven, and so on. All this is presented as the objective essence of a human life - literally what we were created for. To refuse to follow this authentic pattern and model of human life is to deny our God-given nature. It is literally to act unnaturally.
When homosexuality is denounced as 'unnnatural' it is usually the Christian model that informs this view though Islam and Judaism also hold that homosexuality is unnatural - as not what the Creator intended in bringing us into existence.
You correctly point out that violence and anger are 'natural' urges and that this doesn't make them right. I think what Aquinas would say is that homosexuality can be a 'natural' urge in the sense of being something to which people (some people) are inclined involuntarily but that this does not make homosexuality 'natural' in the sense of being any part of the authentic model and pattern of human life. It is a deviation from what God intended, an imperfection in the individual who is inclined towards it even if the inclination is involuntary.
I am not trying to sell Aristotle or Aquinas to you. I just hope I have explained how homosexuality can be both 'natural' in the sense of being involuntary to the individual but 'unnatural', if this is what you think, in the sense of being a deflection from the authentic model and pattern of human life.
Both the examples I have used, Aristotle and Aquinas, belong to the Western tradition of thought. Similar examples could be taken from Eastern thought; I have left them out only because I do not have the expertise to discuss them.
My own views about homosexuality are neither here nor there.