Moderator's answer to the question: Why are other coin interactions with the community prohibited in the Bitcoin subreddit?

0 (moderator):

Let's assume for a moment that Monero is a legitimate altcoin that delivers on its promises of privacy and scalability. These are erroneous assumptions, but we'll just suspend reality for a moment.

We'll have to suspend reality again in order to assume a very productive discussion about "Bitcoin vs Monero" takes place where the pros and cons of each coin are considered. Everybody is happy! But in reality, what actually occurs when we allow such a thread, is that dozens of Monero shills show up to brigade comments, downvote bitcoin advocates who criticize Monero's false marketing claims, and upvote their fellow Monero holders. This happens because users are financially incentivised to suppress criticisms of whatever bags they're holding, no matter how valid they are. But let's pretend that Monero users aren't just shilling their investments.

So, the very productive discussion happens without brigading or manipulation from outsiders. Then what happens? Well, inevitably someone heavily invested in Ethereum will post their own "Bitcoin vs Ethereum" thread. The problem is that there is no way to make the same assumptions about Ethereum actually supporting the onerous marketing claims that are used to promote it. Ethereum is an outright scam and no amount of suspending reality will ever overcome that. And yet, the same bag-holding Ethereum shills will come and spread lies, denigrating Bitcoin in an effort to pump their scam coin.

Then what happens? You've opened the floodgates for tens of thousands of "Bitcoin vs Random Ass Shitcoin" threads. There are over 22,000 shitcoins now, and they're all either outright scams, snakeoil, or simply broken bullshit. Should r/Bitcoin be hosting "Bitcoin vs 1$Boy"? Should we waste our time evaluating the merits of every single shitcoin in existence?

Of course not, that would be absurd.

Granting an exception for 1 shitcoin merely opens the door for bagholders of thousands of random shitcoins to come and shill their bags. So, r/Bitcoin has centered itself as a subreddit that is exclusively dedicated to Bitcoin (as the name implies). Given all the other shitcoin subreddits out there that openly promote these various scams, it's the right move to have at least one place where the promotion or legitimization of those countless scams is prohibited.