So.. don't do it? If anyone with rudimentary SDR knowledge can build a system to interfere with aircraft landing, and they can get away with it by taking basic precautions (don't stay at the scene and don't brag), that's still pretty terrifying.
Anyone with decent opsec and pre-existing domain knowledge can easily get away with it while regular cops are watching or investigating. Yes, this is extremely terrifying. The only real deterrent is that national-security-interest-level investigators will probably take a look after any serious incident occurs, and then the perpetrator would need to have perfect opsec to remain uncaught. (And this might possibly be accomplished by never touching SDR again.)
Anyone without rudimentary opsec will likely be caught between the "shits and giggles" phase of experimentation and the "domestic terrorism" phase of doing something extremely stupid near an airport. This person will likely ask questions on a forum site that are sketchy enough that the regular hobbyists report the suspicious user. This is a pattern that repeats often: stupid criminal gets caught by talking about doing crimes, or by showing criminal behavior to non-criminals. Any crime large enough to require a conspiracy is also large enough to have a secret informant.
The biggest threat is someone with a legitimate interest in SDR, and enough skill to devise an attack unassisted, who experiences a psychological stress powerful enough to make them break, and turn against the civil order. That is extremely low probability, but still theoretically possible. People that decide to pick up a weapon and fight are likely to use what is at hand, and the expertise they already have, to attack. Everyone else in the field has a very strong interest in making sure that no one does anything overtly stupid with SDR, because even accidental missteps could ruin the profession/hobby for everyone, entire countries at a time.
So.. don't do it? If anyone with rudimentary SDR knowledge can build a system to interfere with aircraft landing, and they can get away with it by taking basic precautions (don't stay at the scene and don't brag), that's still pretty terrifying.