They are, for the most part, not the problem as we modelers see it. It's the non-flyer/modeler that sees them as a problem.
An R/C boat is on the water, it's a danger to anyone near the water as well as any wildlife. A nitro or gas boat is even worse due to the engine oil, exhaust and noise
An R/C plane is being flown, it's a danger to everyone since it's going to crash and hit something/someone. If it's not a foam park flyer, it's even more dangerous since it won't crush on impact. A nitro or gas powered plane is even worse since, once again, it's noisy, messy and and potentially deadly.

It's a no win situation since, as long as John Q Public has a cellphone and can come up with a plausible reason to complain, the flyer is almost always going to lose