There are certain things which are prohibited because of danger, many of which are listed here. A good number of them are confirmed by modern science to not cause any (physical) harm (ex. meat and fish, leaving peeled garlic overnight).
I can understand the two extreme approaches:
- Since it's because of a potential danger, if it can be confirmed that there's no danger, then there's no problem with eating it.
- Once Chazal instituted not to eat these foods, then even if the apparent reason is proven false, we still uphold the original prohibition; perhaps there's a different reason they didn't reveal, and even if not, it's not in our authority to overturn decrees of Chazal.
To me, the Shulchan Aruch seems to follow the former approach, as while many Rishonim pasken like the Gemara not to leave peeled garlic uncovered, the Shulchan Aruch doesn't seem to hold that it's an issue (more on that here). Likewise, he paskens that in areas where snakes aren't common, there's no issue of leaving drinks uncovered (YD 116:1). He does list many other things, such as eating meat and fish together, as being dangerous (ibid. §2), but that wasn't known in his time to be otherwise.
What I don't understand is the middle approach – among those which are no longer considered dangerous, some of them are forbidden, and some of them are permitted. This seems hypocritical: at the same time that they insist Gilui is fine since snakes aren't around, they refuse to eat meat with fish. (Admittedly, just my saying that is itself hypocritical.)
What is the logic behind this approach? Is it just blind reading from the Shulchan Aruch, without any thought as to the reason behind the Halachos, or is there an actual reason behind this approach?
(I discuss food in this post only because it seems to come up the most often; the same discussion would apply to, say, walking alone at night in a safe neighborhood.)