It must be noted that these topics are quite lengthy, and you should expect a read when clicking those links. I should also mention that I'm not going to go back into my arguments regarding both rules, as you can read them in those threads. This post is more to chronicle my thoughts regarding the RAW/RAI battle that tends to be fought within the Warhammer 40k community.
In both of those threads, you'll see that I take a primarily RAW stance on rule interpretations. I believe that the rules are more or less sufficiently written to cover almost all of the questions that could come up in a game. There is some things that obviously aren't, because 40k is incredibly complex even in its simplicity, but those are covered in the FAQs that Games Workshop puts out every couple months.
However, with that being said, there are occasions where I'll take a RAI stance. While people will say: "Hey! You need to be consistent or your arguments are not valid!" I would agree with that. That is why when I do take RAI arguments to the table, I back them up with written rules. One example is the Doom of Malan'tai and its Spirit Leech ability. Prior to the FAQ release, there was the argument over whether or not Spirit Leech affected units in transports. Normally, I'd take a RAW stance and say, yes, the rules state that it does affect transports.
However, in this cause, I took the RAI road because this was not how GW intended it to be played. 5th Edition contains quite a few explicit rules stating that literally almost nothing effects units inside a transport, unless it was caused by a vehicle damage result. Now, because a codex special rule is vague enough to glean the possibility of affecting said units in transports, doesn't mean it is so. The special rule does not SPECIFICALLY state that it can do that. So, that is why I took the stance I did, and I turned out to be right.
That brings up another point in this. Games Workshop wrote Warhammer 40k to be a permissive rule set. That means the rule book has a set of rules that specifically outline what happens during the battle. If a situation comes up where you might be able to take an action, but the rule book doesn't say you can, you cannot do said action. Fortunately, the BRB (Big Red Book) is pretty though in its permissions and is generally lax enough to allow most actions. But in the cause of Spirit Leech, the BRB did not allow it to occur, so it shouldn't have.
Coming back to "Kill Them All" and "Righteous Zeal/Going to Ground", the same principle applies. The GW FAQ explained that "KTA" should be used as it was written in the codex, but it was some BT player's contention that because the 5th Edition rulebook didn't contain "Target Priority" testing, you couldn't use the rule. Following my argument in that topic, I break down the rule and show that it does in fact explain exactly what is needed to use the rule and how. The same goes for "Righteous Zeal/Going to Ground."
Another situation occurred recently regarding Drop Pod rules and scattering off the table. It was my contention that such drop pods suffer a Mishap, as falling off the table isn't covered in the Inertial Guidance System special rules. Only enemy/friendly units and impassible terrain. Because the BRB says that the edge of the board is the end of the world, you can safely surmise that this means its a Mishap.
My opponent took the stance that "in real life", there would be more battlefield beyond the edge of the battlefield and would safely land (even though the BRB said otherwise). And that even if there was some abyss of doom right there at the edge, the drop pod's Inertial Guidance System would account for that just like it does for Impassible Terrain/Units. Which would be a fair assumption, had the rulebook not said the not said that the board edge is the end all, be all. That, and the Inertial Guidance System special rules didn't SPECIFICALLY mention it. Drop Pods have been around since the very beginning of 4th Edition. I fairly certain that this rule issue has come up in the 7+ years since then, and if GW had wanted to include it, they would have the opportunity to do so in numerous FAQs and re-releases of each SM codex in that time frame. In the end, I was asked to "Look it up on the internet and see what other people said". Page after page, thread after thread of people saying the same as me didn't convince him. If I was to finish the game, I had "Hand of God" it and fortunately won the roll.
Now, I don't want to be construed as a Rules Lawyer, as I definitely am not. More often than not, if there is a rules or situation debate (such as LOS), I'll give the benefit of the doubt to my opponent. Unless its a big, game-breaking, or changing thing that needs to be addressed (such as Doom). Then I'll ask for a ruling from a Tournament Official. Otherwise, a "Hand of God" is used. I can also be wrong in my interpretations. If I'm proven wrong with an intelligent argument, as I always give, then I'm happy to submit. I have no problem with that in the least.
I play for fun like the rest of everyone else and I don't find any fun from arguing rules with my opponent. It is just plain more fun if the game goes smoothly and you can just enjoy each others' company. I just ask that everyone know the rules before they pretend to be experts at them.
That leads me into INAT. Who do these people think they are, creating rulings for the community? Not only do quite a few of these rulings contradict everything that is said in the BRB, a great many of them have been overturned by Games Workshop themselves via FAQs (though the INAT counsel is relatively quick to change the FAQ to account for these "mistakes")! If you look at the INAT file (Google the latest version), it is totally and completely homebrew 40k. It isn't anything like what Games Workshop designed. How such a group of people were selected to make these rulings, is beyond me, but it is incredibly alarming that so many people take the INAT FAQ as The Word. When it is NOT! Its gotten so bad that most tournaments around the States use it, even though most of the competitive player base loathe it's existence. While some people might say "Just don't go to tournaments where its being used." That is a problem for people who don't live in metro areas where there are multiple stores running tournaments. They don't even have the option. If they want to play in tournaments at all, they are FORCED to live under it. And that isn't fair to the player. Even in metro areas such as where I live, its hard to find a place not using it. But that is enough of my mini-rant on INAT. Just know that I hate it, and I wish Games Workshop would slap a "Cease and Desist" order on them and do a great favor to the competitive community. Leave the ruling decisions to the game company to designed the game.