Under international law, countries have complete and exclusive sovereignty over this airspace, just as they do over their land. They aren’t “taking someone else’s rain” because the clouds they’re seeding are effectively theirs anyway
Less rain than you'd imagine falls on the oceans, due to the land having varying elevation and temperature, whilst the oceans have far more constant elevation and temperature so the conditions needed for rain happen less.
My understanding is that cloud seeding has been going on for quite a while over Texas and the rest of the southern Plains.
It's hidden in plain sight, and the only people who ever seem to talk about it are total wingnuts who also believe things like climate change is real but manufactured by the US and other world power militaries (using secret technology) for geopolitical purposes, often conflating real cloud seeding with variations on the classic chemtrails conspiracy theory.
It's a largely unregulated continent scale weather and climate modification experiment. I haven't booked too deep into the research on it, but because powerful agricultural interests are involved, I'm sure nobody is looking too closely at externalities and would prefer to keep it that way.
It's a way to take someone else's rain.