I don't think realistic is a good excuse, because the shot is framed and posed intentionally to make the panties visible, so the impression isn't realism, it's fan service. I think a realistic version would feel more incidental, but it's hard to describe in words what I think that would look like. That said, even if realism isn't an excuse, I don't think that makes it distasteful, per say.
Mostly I think you should just consider who your audience is. Women are more likely to feel like a story isn't for them if they're seeing panty shots for no particular reason, and similar. I'm drawing a NSFW scene right now for my comic, so Id' feel hypocritical if I was like "no panty shots! always bad!" I think the best you can do is be thoughtful about the tone of your comic, and try to make it feel like it fits the flow of things???
Haha, I really don't know! I definitely don't have any examples, but.. Maybe if it felt incidental, and not like the camera view was trying to sneak a peak. Not overly sexualized. Or a situation where it really fit the mood, ie characters are getting intimate, and it's artfully framed to... enahnce the moment? I don't know, I've never done a panty shot. These are my best attempts at describing a tasteful one. XDDD