I understand the feeling, I only question the adoptees' lack of foresight. It seemed to me like it would be the norm for clans to ask their new adoptees to give their jutsus to the clan. In other words, if I had been accepted into a clan, I would have expected the clan to ask for my jutsus. I can't give an actual quote for that, though, so this impression could very well be wrong.
So clanless shinobi should
never teach techniques to anyone, because that person might join a clan and give away their secrets? This is one of those areas where
while the letter of the law says one thing, the
needs of society require that people just
don't do that. Yes clans
can steal techniques through tactical adoption, but if they
do that then Leaf breaks down even further than it already is. For Leaf as the QMs have portrayed it to
make sense, this is something the clans have the power to do, but refrain from (except when they can do it secretly and get away with it). Certainly
not something a tiny fledgling clan would do if it had any sense, as it would poison the clanless population (and most clanless Jonin who are the ones who come up with those techniques) against them, even
without KEI.
Original techniques/styles/etc are
works of someone's life made through blood, sweat and tears and rooted in experience. They are proof that someone
survived to pass them on to the next generation, and for clanless? They might as well be the one legacy they actually get. This is an emotional reaction that will not make strict logical sense to you; the closest equivalent IRL today would be... the reaction artists have to AI copying their works.
@eaglejarl am I interpreting the society/culture you and the QMs have written correctly?