I agree with the majority of what you say. In particular your point that The emphasise of infantile/childhood sexuality should be on the infantile/childhood, not the sexuality. It is about the boundaries we, as adults, put around it and maintain, to protect children from exploitation...which was my point too, though you made it much more concisely and articulately.
That is really interesting. I don't think we are arguing different things, although I would need to say current trends in pornography are extremely damaging, in my opinion, for young women, and the kind of excrement fantasies you describe are surely some kind of philia,
Of course they are damaging - there is a whole political argument to be had about porn; and there is an argument about where the boundaries between socially healthy and paraphiliac sexuality should lie. But Freud I think would be uneasy with the concept of normality as an organising principle. We know from the work of sexologists and sexual theorists - even feminist theorists like Nancy Friday - that most people have sexual fantasies which are outside the norm. In fact, Freud would say all sexuality is a perversion in that it is a deviation, a swerving away if you will, from original infantile complexes. In fact, it is the 'normal' sexuality that is the perversion. But Freud was also a moral and political conservative who believed civilisation depended on the repression of taboo wishes. In 'Civilisation and its Discontents' he argues that outbreaks of mass barbarism occur when civilisation's repressive mechanisms break down. So he was very much against freeing people from repression per se. Perhaps with porn what we are seeing is the results of those mechanisms being removed on a mass scale, and all of human culture's infantile sexual drives finding expression? Contrary to popular belief, he would see this as an unhealthy thing I think.
As for the necessity of excretory functions and breast feeding, absolutely. Freud's point was that human sexuality develops from our most basis needs. For example, when a child is toilet trained and finds they can withhold or expel excreta at will, and that this is a pleasurable sensation, then they become for the first time an embodied autonomous subject that can control their own pleasure. For Freud this was a sexually developmental stage.
You're absolutely right that the concept of child sexuality is open to abuse. In the 1970's there were circles of people on the radical left who believed we would only be free of bourgeois, capitalist morality once all sexual taboos were smashed. These were people - including some feminists - saying that society wouldn't be free until parents could have sex with their children and people could have sex with animals and all sorts. This was an actual conversation that was happening, believe it or not. All these paedophile liberation groups were founded that were seen as cranks but received nowhere near the opprobrium they would today. I mean can you imagine? It wasn't until a lot of the big abuse scandals broke the 80's and 90's that they truly fell out of favour.
Still, you do get lots of paedophiles justifying their abuse in terms of the child enjoying it or whatever, which is obviously repugnant.
Nevertheless, child sexuality does exist, and it is very important that we understand that so that clear boundaries can be established it and adult sexuality. Arguably, that is not happening at the moment. Look at the way children are being sexualised in our culture? This is exactly what shouldn't be happening.