It is what it is. War is a much more horrible thing than a disinformation campaign. So let’s just make war illegal, problem solved!
Unfortunately it doesn’t work that way.
Whether Russian, Iranian and Chinese disinformation campaigns against America are legitimate or not isn’t all that relevant. They’re happening and will continue to happen regardless of how legitimate anyone considers them to be.
Eventually there may be treaties countries will agree to stop doing disinformation campaigns. But Russia, China, and Iran aren’t going to sign on to these agreements if they’re the only ones with the capability to conduct disinformation campaigns. Why would they give up their capabilities to disrupt their adversaries if their adversaries didn’t have the capability to disrupt their countries with disinformation? Gotta have Mutually Assured Disinformation before you can get everyone to agree to stop these activities.