Actually with certain avionics systems, the danger is quite real. The wrong frequency signal at the wrong time can cause an almost complete restart of many of the aircrafts systems. This is part of the reason why the in-flight entertainment systems have to be purpose built and wired. On the other hand, most of the time it's a bit of extra noise over the radio.

When Sony removed the "Other OS" option from the PS3 they locked people out of a legitimate and relatively safe homebrew environment. Somewhere that people could play with the device without voiding their warranty. It was an option that really "sold" the device to many people who now own one.

While someone would have eventually jail-broken the device, I doubt it would be as widely used as these dongles are; if Sony had (a) left the "Other OS" option in, and (b) possibly added said-option to the "slim" PS3 consoles. The way to combat people jail-braking a device is to give them a safe way to homebrew without the possibility of bricking their consoles or voiding the warranty.