There is nothing wrong with revealing a little skin, especially during hot spring and summer days. I personally know how popular this trend is because I see it on my friends all the time. To this end, cropped tops are having a great popularity among, celebrities and fashion enthusiasts.
I am not naive, I know for a lot of girls the crop top can be about showing off your stomach but I think there are perfectly feminine, and elegant outfit choices that can reveal a bit of a toned midriff, and not be too trashy.