It is hard to say what is directly right or wrong when it comes to modding, as it’s something developed by the community, not the owner of the product being modified.
I realize now that I’ve written one hell of an essay on the topic and I hope I don’t bore anyone! Sorry ahead of time. If I have any typos things you want addressed, let me know 
Addressing Prior Points
What makes the modding community great is that they are doing it of their own volition; anything created is (usually) made only to be enjoyed by themselves or others. Most modders create content for joy; there’s no need for money/recognition because they had fun creating it and have even more fun enjoying the results. Game studios tend to react poorly to it but that’s probably got more to do with gameplay reasons than being oppressive in some way.
Bingo. I think what he was addressing was that it will damage the modding community for that game in particular, but I think that a modding community as a whole would just shift their attention to a different title (or, if they enjoy the base game enough, they just won’t care because mods aren’t necessary).
Valve is certainly doing it a way. I can’t tell you whether it is strictly right or wrong, but I certainly enjoy their cosmetic market for Dota2. I think it provides an awesome avenue for graphic designers to output incredible works of art and be recognized for it! This, however, cannot be the way most mods occur… cosmetics and gameplay mods are two entirely different beasts.
Devs are, as I can understand it, likely unable to integrate anyones gameplay mods into their game. They can have an ‘Active Mod List’ where you can turn it on and off, but I don’t believe a dev can say “Okay, we voted for you, now I am going to make your code part of my game” and sell it like they do on the Dota2 cosmetic market. Most non-cosmetic mods don’t just add to core gameplay; they change core gameplay and can also subtract from core gameplay. Can’t integrate things like that into a game unless you intend to make the change permanent… but at that point you aren’t approving a mod for a game, you are patching it.
I think this is a very good point to make! Most games that heavily-lean on community modding tend to have very strong, dedicated groups of gamers. Most games that are like this are also single-player. Players are pleased with access to play the game their way, pleased players get their friends to play with all of the awesome mods, and the life of the game is extended with the only cost being to the players. Seems like a pretty huge benefit to me (cough-cough-Skyrim-cough-cough-Fallout-cough).
However, I do have an issue with @Haxorzist’s statement in the final 5 words. The community of many games that depend on mods for additional content are allowed to do anything, but that doesn’t mean every modding community must be allowed to do anything they please.
Modding Details and Modding Implementation Trends/Styles
In Fallout/Skyrim/TF2/Witcher 3/XCOM/Mass Effect/Subnautica/Darkest Dungeon/Divinity/Dragon Age, we can mod pretty much anything we want (which is amazing). However, that doesn’t mean that every game has to let us do whatever we want; let’s note that every game we see here is single-player (for the most part) and has no heavy-emphasis on multiplayer.
There are many games that are multiplayer, but very few of them allow gameplay mods. Any competitive game that’s played online will likely not allow mods, and if they do the mods are almost always cosmetic. This is because the Development team cannot allow mods to change their online gameplay unless it’s an opt-in scenario… and in almost all of the games where you have mods, there are “Modded Servers.” Rust/Minecraft/Terraria/TF2 all have gameplay mods and modded servers, but they are all opt-in. This should ring a bell, because it’s what Vermintide 2 does.
Luckily for us, FatShark has taken the trend a step further (which is WONDERFUL, by the way) by allowing a list of sanctioned mods. Most of them edit the UI, Menus, or Key-Bindings in some way… which is awesome. We now have additional content in the base-game… and it’s still opt-in. Note that they haven’t integrated any mods that change gameplay… and it’s because it would be an absolute nightmare to do so.
Addressing the Title of the Thread
It is impossible what is to be qualified as right and wrong in the case of mods, but fairness is pretty easy as I see it. Please know I am trying to address this as unbiased as I can, but that I’m also human and flawed.
It is fair for a Studio/Publisher to ignore anyone wanting to mod their game; it is their product and they do not have to approve/encourage anything that anyone does in an attempt to mod the game, for better or for worse.
I think that, depending on the game, it is desirable for a Studio/Publisher to create a game where we can mod it as we please because it doesn’t detract from anyone else’s gameplay experience; if it does detract from anyone’s gameplay experience, it will reverse that desire. I am guessing that this is why most desirable Studios/Publishers who do this are producing single-player oriented games.
I think that, depending on the game, it is desirable for a Studio/Publisher to create a game where we can enjoy modded-gameplay on an opt-in basis because a modded game cannot detract from gameplay; this is only true because anyone playing a modded game has opted-in, otherwise it will reverse that desire. I am guessing that this is why most desirable Studios/Publishers who do this are producing creative/cooperative multiplayer oriented games.
I think that, depending on the game, it is desirable for a Studio/Publisher to create a game where we cannot mod it or edit gameplay; instead, it is up to the studio to deliver the experience we want. If they fail to prevent mods/hackers from damaging my experience, it will reverse that desire. I am guessing that this is why most desirable Studios/Publishers who do this are producing strictly multiplayer, competitive games.
However, I like mods! I think they are fun and cool and I love it when someone replaces the Uzi in CS:GO with a kitten that shoots hearts out of it’s eyeballs because it doesn’t change how the game is played and it’s hilarious!
I also love cooperative/creative games, because that’s just where my heart lives. With that in mind:
I think my favorite sort of Studio/Publisher is one who creates a cooperative/creative game and allows mods on an opt-in basis.
FatShark has done that and has also allowed sanctioned mods into their game because it doesn’t conflict with what makes a Studio/Publisher less desirable for a cooperative/creative game. Your mods don’t hurt my experience, so FatShark has opened the door. That’s… pretty amazing in my book.
TL;DR: I believe that, for the model of game that FatShark is pursuing, they have one of the best (if not the best) models for allowing mods on their game.