But not all cultures and people see it that way, whether they just don't or choose not to.
It's not an issue of "nudity should be a beautiful expression of the human form!" it's just "respect the general consensus of all ages and don't try and shove stuff that could be considered inappropriate, even if you find it artistic, into other people's faces."
This isn't aimed at just you specifically though, I see this happen everywhere - "well I'm not gonna mark it NSFW because I believe nudity is an art form!" Yeah, well, it's not about what you think. It's about what kind of respect you have for your readers, of all ages and cultures. For all you know, there could be 10 year olds finding your comic. Do you think they - or their parents - would appreciate coming across a page that's not marked NSFW when it probably should be for full frontal nudity?
I don't see anything "beautiful" about the nude form. Not saying I sexualize it either. I just find it is what it is - a naked body. I can get why others do, and why in certain situations, it can convey the mood of your story, but I, personally, couldn't care less how artistic or beautiful it is. I actually find violent scenes with lots of fighting and anger a lot more expressive than the naked or even sexual ones. Am I a bad person or completely wrong for saying that? Probably. But that's my opinion. Am I going to let my opinion sway what I decide should be filtered out for my readers? No. I've had kids and young teenagers read Time Gate before. I am friends with some of these teenagers, some people I just got really along with, others family members. I've met middle school kids on the side of the street tell me they read Uzuki and Time Gate, both of which have had their NSFW moments, from touchy content to people getting their heads ripped off! I love those scenes for their moments, but I'm not going to let my objective views on nudity, sex, violence, etc. sway what I show my readers. It will still be there - but they will have to make the decision whether they want to see it or not.
NSFW gives readers a choice. It is not "cutting the reader off" or censoring your work. And that, to me, is a lot better than just deciding "nah it'll be fine people need to know this content is okay to me". You won't lose any readers that way, either. I don't put my art and content on such a high pedestal as to disrespect my younger or more sensitive readers by showing them stuff they would probably rather have a choice in seeing, stuff that I thought was fine because "NO i don't want to censor my art, you can't make me!!"
And in the end, you need to do it with a respect for Tapastic as well. In the end, these are the guys keeping us here and helping us grow. As someone pointed out already, they really encourage people use NSFW whenever it's possible and appropriate, because if they don't, their iOS app which they worked so hard to achieve could be booted by breaking Apple's hosting rules, and with that gone, Tapastic would be taking a HUGE an UNNECESSARY step backwards.
It's not about your opinions. It's about respect for everyone and giving them the choice they should be allowed to have, no matter how "artistic" and "beautiful" a mood you're trying to convey and feel that nudity/violence/whatever contributes to that. Their feelings should come after they've read those pages - after they've chosen to.