The "joys" of unintended reaction fire... from a rocket launcher.
Said dangerous weapons are usually 2-hand restrictive (red 2 number). Personally, I worked around this by assigning a side arm on the other hand (thus providing some sort of self defense) or perhaps a motion scanner as well, to remain useful in close quarters. But the TU loss of putting away and pulling out said extra item sometimes makes the difference.
I use the right-click priority hand for ranged weapons a lot. For example, in Piratez (current mod I'm playing) where I right click on the MG of the 85 mm Tank, so, if it react-fire, it's with the machine gun and not the main cannon, which could blow up the whole squad. Same with the Heavy Lascannon tank, where I select the tiny laser machine gun instead of the main gun, thus preventing wasting ammo on non-value targets. It's worth to note that the default weapon also controls the reserve TUs check for firing, which is nice.
I haven't tested, so I don't know if it were to right click on an empty hand, while holding, say a Rocket Launcher on the other, will prevent reaction fire, or the game will just switch to the other hand if the default hand is empty regardless of priority. I think it's the latter.
I agree with the OP idea, maybe a weapon safety (via options) can be implemented that instead of defaulting the weapon, will
negate the weapon, on the selected hand for a reaction fire ranged attack. This can be just another right click, perhaps this time showing a red dot, will act as a weapon that won't automatic react-fire. Thus the sequence of right-clicks could be:
1st right click: yellow dot = default hand for reaction fire
2nd right click: red dot = hand forbidden of reaction fire (aka gun safety)
3rd right click: clear = all normal.