Really hate that fanon.
The Citadel has laws regulating the development and creation of AIs, not laws forbidding their existence.
Uh, it's not fanon.
Granted this occurred in the immediate aftermath of the Morning War but there's really no way to paint this as anything other than the genocide of an entire category of lifeform because one species participated in self defense and what the Geth did was self-defense, that the war resulted in such horrific casualties doesn't change that fact. In Mass Effect 1 Tali describes the Geth as being on the cusp of revolt but as Mass Effect 2 and 3 show that's not true.
We know thanks to Mass Effect 3 that the Geth fought solely to preserve their own existence and even then only after significant losses to the Geth and Quarian sympathizers. It's tragic that the first reactions by those responsible for the Geth peacefully reaching out to them with the philosophical question of "does this unit have a soul?" was to ascertain that the Geth were becoming sentient and thus would rise up for being treated as slaves rather than attempting to communicate. One would think if the Quarians had the foresight to realize that a sentient being might consider such servitude as slavery that they might also consider being destroyed as murder.
The saddest part is that Mass Effect 3 shows the nascent intelligent Geth of the Morning War weren't any less willing to serve and reacted with confusion, one Geth in particular gives these rather heart wrenching pleas, asking what it isn't doing right and how it can reprogram itself to properly serve just as it's shut off to be examined. Given the mindset of the Geth as depicted in Mass Effect 2 there is every chance the Geth would have been okay with the master-servant relationship that they had. There's even an instance in Mass Effect 3 of a Geth platform trying to surrender itself when it discovered that its owner was putting itself at risk by hiding it.
Equally the idea that the Geth are pro-AI is incorrect. The Geth are pro-Geth. Nothing more or less.
That's not quite true either. We know the Geth actually care in their own way for their creators as shown by their actions in the lead up to, during, and after the Morning War. Though the Geth did wage war to preserve themselves didn't do so at the cost of their creators and let the Quarians escape at the end of the conflict. In Mass Effect 2 Legion explains how the Geth act as caretakers for former Quarian worlds, likening them to places such as Wadi-es Salaam, Arlington, Rookwood, Tyne Cot, Piskarevskoye, and Auschwitz and as Shepard points out given how the Geth view their own mortality those memorials are not for lost Geth.
The Geth value self-determinism and now that I think about it they would probably appreciate the spirit of the Prime Directive. Their lack of experience when it comes to organic life likely also contributes to them avoiding direct contact in favor of remote observation. They're isolationists but I don't get the sense that they're indifferent to others in the galaxy. I think they're curious but fearful and with reason. Legion explains it best in one of the conversations if you bring him to Tali's loyalty mission. When Admiral Koris asks him if the Geth would be open to the idea of peace Legion says he doesn't know if peace is something that is possible between their people without further information and goes on to say,
"When the creators have believed victory is possible, they have attacked us 100 percent of the time."
This is arguably also the case with the Citadel races given what they did in their own space in the aftermath of the Morning War. The Geth can't predict how the Citadel or the Quarians are bound to act because they can't accurately predict their thought processes. Their alternative then is to use previous experiences to try an extrapolate a future outcome with statistics. It is not hard to see why then a race of machines would be wary of making contact with either of these parties as the numbers would indicate favorable outcomes to be unlikely. An unknown would be more favorable if only because they wouldn't have a previous confirmed negative interaction and thus swing the prediction in the negative direction.
Of course the fact that the Geth have killed everyone that entered their space is somewhat incongruous with this interpretation of the Geth. The meta answer is that the Geth being more than future Skynet was written up after the first game.
One possible explanation is that it has been the Reaper aligned Heretics that have killed all those that have attempted to make contact with the Geth. We do not know when exactly it was that Sovereign first contacted the Geth and offered to house them in a Reaper shell, it could have been during Saren's lifetime or it could have been just after the conclusion of the Morning War, there's just no telling, but it would make some sense if all the Geth people have encountered since the conflict were Reaper followers.
It would have been in Sovereign's interests to prevent the greater galaxy from making contact with the True Geth both to keep them isolated and from helping strengthen the rest of the galaxy and since the True Geth would have no reason not to share with others his existence. Given the True Geth kept themselves intentionally kept themselves separate from the Heretics it would not have been difficult for the Heretics to position themselves along the borders of the Perseus Veil so as to intercept any vessels headed into former Quarian and True Geth space.
Edit:
What's hilarious is that the whole evil genocidal AI is a thing in Star Trek too. There's enough of them to have a whole asylum for them, but the Federation is just like 'well some AI come out insane. It socks but what can ya do'
Yeah, by this reasoning Starfleet should pre-arrest their flag officers given how often their Admirals go rogue.