I actually agree with you, but it draws the logical conclusion that if someone with schizophrenia can't be trusted with a firearm should they really be free to roam the streets at all?
I've seen you say this before. But I don't think that conclusion is logical at all. This seems to ignore the rapid and impulsive nature of firearm use and the ability to target at distance while imparting a large amount of lethality in a short period of time. Compared to not having that tool.
Schizophrenics and multiple other people exist in transient states of stability in which they should not have access to firearms sometimes and other times probably could manage.
You'll argue the other ways they can harm people, but very few encompass all the things that include the portability, lethality, ability to project violence at distance. Other things that can match a firearm include more complex schemes that increasingly become difficult for a psychotic patient to put together, especially without causing undue attention to prevent it while in process of developing. This stands in stark comparison to a gun standing by with a trigger pull.
The closest argument would be the ability to do something like a speeding vehicle, but even that finds physical limitation in portability to getting a vehicle into a crowded space for maximal carnage.
Complex bomb making and planting, etc would require someone with a baseline nefarious plot and with that, correct, said person should not have access to guns. But that's not schizophrenics who simply battle with transient delusions and hallucinations.
And none of this touches suicide, which has reasonably good data for completion with presence of firearms above the baseline regardless.