I’ve generally been on the anti-gun side, simply out of preference, as I’d like LotC to be more LotR-fantasy-themed than something akin to Warhammer. That being said, there are some good arguments on both sides, though also quite a few flawed ones. One is pointing out the social structures being unrealistic in a medieval setting -> therefore server is not “medieval” fantasy -> therefore we should have guns.
The medieval fantasy theme is a well-established, but loosely-defined theme that is identifiable across many genres. The fact that most of the governments and economic structures of LotC are not completely based in medieval realism, doesn’t inherently discredit the setting, to be chucked aside, and used as an excuse to implement later-period firearms to the server. After all, the setting is not strictly medieval, but also has fantasy elements in it, to a greater or lesser extent. It can for instance be argued that some power structures or elements in Lord of the Rings are modern, and yet no one would bat an eye if you chose to call it medieval fantasy.
That being said, pointing to social structures in order to justify the implementation of a technology is pointless, as the interaction between history and technology in LotC has never strictly mirrored that of real life. The consideration should instead be based in preference of the players. As such, the simple “I don’t want guns in my fantasy setting, because I don’t like said fantasy setting” might not be an argument, but it is still a valid point that should be taken into consideration.
Mechanics-wise however, I don’t see that many issues with the implementation of guns. If the same standards applied to crossbows are applied to guns as well, powergaming shouldn’t be an issue. What should be addressed however, is what kind of gun we’re talking about specifically. Unlike crossbows, most firearms will pierce good-quality plate (which is one of the factors for why it became obsolete later in history ofc), and can in this regard outclass the bow and crossbow. Should the guns ever be implemented, they must be so with significant nerfs, to not become the only viable alternative for ranged combat.