What's explicit?
It's often-said in the US that the nipple and areola are defined "sexually-explicit". A women can go to a clothing-required beach and display every part of the breast except for the nipple and areola. Why? And why can men, who have the same EXACT breast structure (except for the milk ducts which are under the skin and therefore never seen anyway), show off their breasts without offense to anyone and nobody asking them to cover their breasts? And don't you dare say size -- there are a lot of (fat) men who would put most women, even well-endowed women, to shame in breast size.
So why is it that women must cover their breasts? If you're one of the people who claim that the breast is "sexually-explicit", can you please define that for me? Because I'm not ashamed to admit that I don't understand that. Other body parts, such as legs, buttocks (women are allowed to wear thongs in public), and earlobes are erogenous zones and are often sexualized and involved in sexual activities, but those are not required to be covered at all times. What makes the breast so different? Specifically, what makes the nipple and areola so different?
Perhaps if we didn't require women to cover their breasts at all times, and people actually grew up seeing women with uncovered breasts, then it wouldn't be such a shock or such a big deal, and it wouldn't be viewed the way it is today. Then again, a lot of good God-fearing Christians* still think that sex itself is the devil's work, so I'm not holding my breath.
* This is not an indictment of all Christians or religious people, only the puritanical and stupid ones. After all, if God created us in His image, shouldn't we celebrate our bodies instead of being ashamed of them?