You're right, there is a huge difference between between illegal content and distasteful but protected speech. Yet you seem to be lumping them together in your post...
Inside your link it says, for something to be considered "obscene":
>The Miller test stems from Miller v. California, 413 U.S. 15 (1973), in which the US Supreme Court held that material is obscene if each of the following factors is satisfied:
>1) Whether the average person, applying contemporary community standards, would find that the work, taken as a whole, appeals to the prurient interest;
>2) Whether the work depicts/describes, in a patently offensive way, sexual conduct specifically defined by applicable law;
>3) Whether the work, taken as a whole, lacks serious literary, artistic, political, or scientific value.
So, by law ALL THREE of the "obscene" criteria have to be met for it to be considered obscene. I want to focus in on #2, because I don't think pictures of children in bathing suits is sexual in nature. If it were, then taking your children out in public wearing said bathing suit would be illegal too... Now, people looking at those pictures may be sexualizing these images in the head, but the images themselves break no laws and show no nudity. So why exactly is reddit drawing the line there? Also, why is Toddlers in Tiaras fine? (there's a subreddit for that too). I don't understand what makes it so different to you (and to reddit admins).
I kept reading and further down in your link it says:
>Child pornography is any visual depiction, where "(A) the producing of such visual depiction involves the use of a minor [under 18] engaging in sexually explicit conduct; and (B) such visual depiction is of such conduct." 18 U.S.C. § 2252 The law prohibits knowingly possessing or transmitting (including by computer) child pornography.
I'm positive that children in swimsuits does not constitute being sexually explicit, so I'm still not getting why you are considering it illegal...
Finally, you say >when reddit (finally) decides to crack down on something that is plainly not legal speech
Yet, based on the legal definition that you provided these subreddits, for the most part, are participating in legal, albeit creepy, speech. Anything illegal has been removed and delt with according to law. Not sure who the real fear monger is here, but calling pictures of children in bathing suits "not legal speech" is disingenuous at best.