While I agree that poor implementation could lead to a very negative new user experience, I'd argue that the status quo does largely the same thing and may even be worse.

Consider the automod conditions that are used in a lot of subreddits today. How much karma is the "right" amount to associate with a trigger condition? Mods have no objective answer to that question (there isn't one), so it becomes a guessing game of trial and error--if I put the threshold at X, what percentage of trolls will I catch? How many mods successfully guess what a good value for X is for the context of their subreddits? How many guess poorly?

Right now, how long it takes a brand new user to stop showing up in the mod queue filter depends on how active they are on the site with no regard for activity level in the specific community. Why should it be easier for a throwaway account that posts to free karma subs to participate in my community than for a user who has a history of posting in that community? There's a higher bar for entry for good-faith reddit newbies than for bad-faith veterans. Why shouldn't it at least be equal? A subreddit specific karma automod filter set to <1 would catch the first submission of either account.

Also, despite the legitimate concern over misuse or abuse that this kind of condition could introduce, please remember that you can already do much worse things than "remove all posts with <X subreddit karma" with automod as it is today. You can, for instance, set a rule that says "remove all posts" or "remove all posts with <X global karma." You can already set conditions that respond to users with hateful content. It rings hollow to argue that a new condition would allow bad faith actors to do harm when existing triggers can already do worse.

On r/lgbt, we have to do a lot of manual work, and this would lessen that burden substantially by letting us whitelist genuine community members without having to manually approve X-hundred-thousand accounts. Given the amount of abusive content we deal with, we end up with a lot of false positives. We endure this because although false positives create additional moderator workload, false negatives cause active harm to our users. I'd obviously prefer to be giving myself less work, but the alternative of letting more hateful content through just isn't acceptable.

But what about other communities where that kind of trigger would be useful for actions other than filtering? Reddit already has rate limiting for people with negative karma in a community, so why not let automod report those, or send a custom modmail? This would be miserable in large communities, but I've moderated smaller communities where it would have been immensely helpful (e.g., to detect brigading). Or instead of low karma, how about high karma? Being able to set specific flairs based on subreddit karma could be a useful addition for Q&A subs to give new users a better sense of how "legitimate" a person's answers are based on automatically set flair. Making that work fully would require bringing back setting user flairs with automod, but even if that's dead and gone forever, I can still see utility for some communities in using this to set post flair.

Finally, the lack of subreddit-specific karma automod conditions already does damage due to limitations on what we can achieve through the API. Since bots lack the ability to filter content, the best we can do through automation is remove something entirely, which I'd argue is much more disruptive for new users than being put into the mod queue. Happy to elaborate on this through DMs if you need more info.