Robert Hanssen was an nth generation white American from Chicago, the son of a cop, and he sold out intelligence operatives (who were later murdered) just for cash. Aldrich Ames: similar story.
Thing 1 was an object with no gun powder in it and it exploded. Thing 2: similar story.
This is a logical error related to the difference between the converse and the contrapositive. There may be a relationship where A implies a greater likelihood of B. Finding various examples of Not_A where B occurs can be rhetorically effective but it isn't sound reasoning to argue that show A does not imply a greater likelihood of B.
And I respect the ideology of once some someone is a citizen, they should have full rights. Though ideology and practicality do not always meet efficiently and in something like this I feel practicality is needed.
So circling back for clarity, my point was I suspect (note, saying I suspect not know) there is higher risk of a naturalised citizen harbouring loyalty to their origin country and/or being more easily manipulated via family ties etc. This would vary by country and circumstance so is not black and white but in this situation where you know Chinese agents are very active, I find it amazing, for right or wrong, an agency would take that chance. And with hindsight, this is a very correct view.
If you want to assert that, you'll need to back it up with evidence. Until you do, there's no reason to assume it -- if anything, one could flip your logic around and claim that birth citizenship should correlate with higher risk since a born citizen didn't have to do anything to "earn" it and so doesn't value their citizenship/country as much as someone who had to put in significant effort and jump through a lot of hoops to get naturalized.
No, it's not.
There is a way of limiting the severity of such a situation though; just caveat the clearance so the bearer is restricted from accessing any information relating to their country of origin (or any other countries they or close relatives have a potential conflict with). It seems surprising that wasn't done here, regardless of his original intent.