This is a self-feeding loop, since introducing a solution can spawn many other problems, known as "bugs". Our solution isn't necessarily perfect.
And we notice things which annoy us. One of them is when new people show up, they have the same problem StackOverflow has - they're used to a certain format, but we work in another format. In some chat rooms (especially MMO chats for some reason), it's common practice to say things like "anybody here?" or "can anybody help me with X?" or "can anybody help me?", or maybe they just randomly select someone and ask. But we don't quite like it. We're here to answer questions. We can't answer your question...if we don't know what it is. Answering these questions produces 0 value in general, and just aggravates us because we see them over and over and over...
We notice a pattern, we notice a problem. We're now at the second step to solving it: https://github.com/Zirak/SO-ChatBot/issues/39 And we have the technology.
So we make a system. It had bugs, the community complained. They were so severe, we shut the system down, only two days after it was launched. But we didn't give up. We improved the system, we fixed bugs, we considered edge cases. 9 days later, it was live again. A month later, the system got improved again.
Can the system be better? Certainly! It still has bugs, it can still be improved, it can be more meticulous about who it welcomes and who it doesn't using better metrics. Heck, it might even have cross-site problems, since I really just made it for the SO chat, not SE in general. However, the important fact here is that it solves a real problem we had. Before it, we had to say "please don't ask to ask, just ask" about four dozen times a week. Now, it's a lot less (because some people either manage to forget, or need a reminder). Just today, when I was catching up to the whole story, someone came in and showed us the problem again.
To conclude, I'd like to say how community driven the bot is. Benjamin Gruenbaum said it before me, and I'd like to repeat: The bot is shaped by the community. We have an active and healthy discussion going around for every suggestion. If we see something isn't going well, we talk about it and improve. Features were added and removed, features were thrown away at planning stage, and it's all community driven. We also ask moderators (one of SO's mods is also a regular in the room) in some gray areas, ask for their approval. We do all this because we're programmers. Our job, our source of fun, is identifying problems, and solving them. So I'd like to ask the moderators to reconsider making this site-wide. Since they're the people who make the rules, my next commit is going to respect that and remove the auto-welcome. But it won't feel right, and it won't feel fair.