While I don't particularly like generic welcome messages (and for the sake of disclosure I should say that I used to leave them for new users, I don't anymore, so I've been on both sides), I don't agree that we should begin flagging them for deletion. It's not because I love them, as I noted, but I have a few concerns about making this a blanket requirement.
- What if the comment containing the welcome message also contains information explicitly relevant to the question? Do I want to delete that too? Personally, I do not. Relevant info to the question supersedes a generic welcome message.
- We're never going to catch all of the welcome messages. Even if we have folks that read every single question that comes through the feed, some may disagree with a policy of flagging welcome messages and simply leave the question alone.
- Our mods are very busy with the tasks they already have. Do we want to add a task that could (COULD) be high volume to their already full plates? I mean, if it were an extremely important issue, such as Should we flag profanity on the site?, that's one thing. But flagging welcome messages just seems like modly busy work. Most people do not like busy work. Perhaps one of the mods will speak to this issue themselves.
I think it's fine to discourage users from leaving welcome messages, if that is the community consensus, but to start expecting people to report welcome messages is out of the scope of the site's requirements.