The purpose of the First Posts queue
The only users who can actively delete anything from that queue are moderators, and that's simply because it doesn't make sense for them to flag something for themselves or go out of their way to perform an action they should be able to perform wherever they see the post. It's not built to be a deletion queue.
The queue exists as a quality check mechanism. These are the first posts coming in to our site from these users, and it's helpful to have a set of eyes say "looks good" or "this could use some attention." All you're doing there is raising a signal fire when something looks off, so that it can be pushed in front of someone else's eyes to be fixed, depending on what the issue was.
Flagging as spam achieves that goal. Spam and offensive flags go directly to the top of the moderator flag queue, regardless of age or how many flags are on the post. They always go straight to the top, because they're important. They also generally get handled pretty quickly once they're at the top of that queue. Quickly enough that I rarely ever see them sitting there.
Some history on spam/offensive flags
Long ago, these flags used to appear in the 10k flags queue as well. But a massive problem arose here in that putting a post in front of a bunch of users with any sort of "spam" label on it almost always resulted in that post being deleted as spam - even if it shouldn't have been. Eventually spam and offensive flags got removed from the 10k flag queue and only shown to moderators.
We don't want a similar thing to happen in review. We already have a problem of users who see that message and just automatically flag it as spam. I've even seen some of them ask about it on Meta - why it was there, and why the system wanted them to flag it. While the message was meant to be an eye-opener and make you look at the post twice, it does have some harmful side-effects on occasion. But by simply raising a flag and letting the moderators handle it, we're limiting the damage to just a bad flag on a post that wasn't quite spam, rather than a post that erroneously got deleted, locked, potentially cost a user 100 reputation, and probably triggered an IP hobble.
In contrast, the worst thing that happens if a post gets deleted as not an answer is that the post gets deleted.
Not everyone cares as much as you
There's a large combination of factors out there for why we don't want regular users "reviewing" spam/offensive flags - people who don't understand when to use the flags, people who just plain get confused, etc. But above all, there are sometimes people who just don't care - the robo-reviewers, the people who just like flagging things for badges, etc.
Moderators care. If they didn't care, they wouldn't be moderators much longer. And it takes quite a bit of care to handle these flags correctly, given that they have some pretty detrimental effects to the user when they are deemed valid and the post is deleted, not all of which the moderators can undo (if it triggers an IP block, they have to get staff involved).
I'm not saying your request is being declined - I'm saying that we'd be very, very reluctant to make a change such as this, because we've seen what effect that label can have on a user's ability to handle posts effectively and fairly, and because they tend to get handled quickly enough that the additional complications to the system are not needed.
Keep in mind as well that any user who encounters posts like this through natural use of the site can still flag directly on the post. You want it deleted quickly, but it only needs to be deleted quickly if there are a lot of users looking at it. But if there are a lot of users looking at it, then it's already more likely to attract a lot more flags in a short time from those looking at it. If no one is looking at it, then there's not exactly a rush to get it removed, because no one is seeing it anyways.
