Man of Honour
Some fathers would at least try to
i) Respect their adult child's right to make their own decisions about their own life and support them in doing so.
and
ii) Evaluate the situation rationally (see below).
Note that the person you're replying to didn't say that he would do so. He said that he hoped he'd be able to. So he's self-aware enough to know that his irrational responses would conflict with his rational responses and that he might not be able to be rational and supportive about it due to irrationality and social condtioning.
I'll elaborate on evaluating the situation rationally.
We're all conditioned into irrational responses regarding sex, with some different responses based on sexism.
While it's no longer true in this country that women who have sex outside of marriage are seen as being pariahs who should be disowned by any family that isn't of very low status itself, there is still some degree of stigmatisation of women who are more promiscuous than social norms allow and especially if they make money from sex. To some extent, the opposite is true of socialised perceptions of men. So it would be a common irrational reponse to be more offended by a daughter going into porn than by a son doing so and respond with some mixture of shame and anger (for her bringing dishonour to the family, even if you don't consciously think about it in those terms) and an irrational addition to protectiveness (partly due to the usual sexism and partly due to the perceived extra harm caused by socialised responses).
Then there's the more generalised stigmatisation of porn, which causes some degree of irrationality when evaluating it as a means of earning a living. Sure, I'd like to think that any child of mine could choose to have either a high-status job and wealth or a job with very high social status in at least some ways (e.g. a doctor with Medicins san Frontieres) and enough money to not have to worry much about money. That's possible for a tiny minority of people, but not for the great majority of people. For most people, the available options are the dole or a soul-destroying job as a minimum wage flunkey. Is working in porn by choice for much more money and a chance of becoming rich, maybe even lottery-winner rich, really worse than a lifetime on the social or as a minimum wage flunkey, constantly worrying about any unforeseen expense, even just a couple of hundred quid, that could tip you over the edge into spiralling debt?
There are rational concerns about someone choosing to go into the porn business as a performer, but not all concerns are rational. Not by a long chalk.
