A lot of people that I know enjoy showing their spanked bottoms off on the internet would rather not also show what’s between their legs. So they usually wear underwear — often the underwear that covers the least amount possible. Thongs, usually. And if they aren’t wearing underwear, they keep their legs together. After all, while I certainly appreciate nudity, I don’t need to see it to enjoy a well-spanked backside.
I wish I could share some photos I’ve seen on Fetlife lately, but that would be against the TOS, so you’ll just have to imagine with me. Sometimes I see images from a certain spanker showing the red bottom of his play partner. Often she is wearing a butt plug. Is that more or less modest than if I were to see between her cheeks? On the one hand, I can’t actually see what’s going on because the plug is blocking it; on the other, wearing a butt plug is an inherently sexual act, and generally engaging in sexual activity where people can see it is considered less modest.
On the other hand, you have studios like Realspankings, where the models are compensated and made aware beforehand if they will or won’t be showing anything. So you end up with images like this:

But, again, these are models who are compensated. A lot of people just want to show off their spanked butts and nothing else. Like in this photo that I found on the internets:

The spankee is wearing a thong to reveal as much of her bottom as possible while still maintaining her modesty. But to some people, even this would be immodest — even though you can see much more than this at the beach sometimes.
And for certain people, modesty can mean showing off one thing but not the other — for example, showing off sexual organs but not the anus. Reasons vary as to why.
Modesty is a sliding scale, really; what is modest to some is immodest to others. For some people it’s modest to be completely spread open but wearing a butt plug; for others it’s keeping your legs together but being bottomless; for others still it’s wearing underwear; and, of course, you have people who don’t get naked in public or on the internet at all. And let’s not forget that modesty can be situational; I generally wouldn’t walk around a kink event like Frolicon with my penis hanging out for all to see (not that there’s anything wrong with that; it’s just not my thing), but a few years ago when I was at an oral sex play party at Frolicon I lifted my kilt and anyone walking by was able to see me getting head. I still consider myself rather modest, but in that situation there was no need for modesty.
By the way, I figured I’d ask my NSFW AI image generator for “spread cheeks with butt plug”, trying to find something appropriate for the paragraph above, and this is what it came up with.

Clearly the technology isn’t quite right yet…
