The idea that breasts are exclusively a sexual "plaything" is the only reason why people have trouble with breast feeding. There are women in other cultures who don't wear bras or any clothing material over their breasts because they're not seen as sexual. And when people of cultural backgrounds who were raised to believe they're only good for sex saw it, they flipped their shit because they didn't know any better.
Now, it can't be denied that on a primitive level, breasts are somewhat designed for sexual attraction. When you get down to the core of why people choose a woman for their sexual partner, it somewhat comes down to her "child baring" body. If a woman's body doesn't show that's she's fit for reproduction, people skip over to the one that is, and a key sign is ample breasts and wide child baring hips. There in lies why people think they should be covered up and out of sight.
Anyone with any common sense knows that breasts are apart of reproduction and sustaining life. Before formulas were created, people had to deal with the knowledge that breast feeding was the only option. Even people who are from cultures without the knowledge of formulas know that breast feeding is natural and 100% acceptable. They're designed for what we use them for, whether people want to open their eyes to it or not. If they have a problem with it, don't watch. It's that simple.
There's this whole taboo about women's breasts that I won't go into but you get the picture.