We've tested salt and know its effects on humans. It would make sense to require new things to be verified as safe before we start putting them in our food, and banned until that's done.
It would make sense, and is therefore done extensively. Glyphosate got approved in a much more lenient regulatory climate (almost half a century ago!) than what we have today but even so its initial approval required safety studies. Furthermore, it is subject to constant scrutiny and its recent reapproval by the EU was discussed heatedly, despite its stellar safety record in the decades it has been used.