Maybe the OP could have done her bit to reverse "societal conditioning" and taken her top off in solidarity with the breastfeeding woman.
Fine, we are socially conditioned to wear clothes that cover certain parts of our bodies. That is something that has evolved over an extremely long time. It's a bit artificial to expect everyone to shout "Bollocks to social norms!" and whip off their clothes and run naked down the highstreet.
There are parts of my body that I simply don't see the need to have on display. There's no practical purpose to it. I don't wear clothes that reveal my stomach. I wear short skirts, but not spectacularly short ones. I don't walk about in bra tops. I don't wear things that are so low cut you can see the tops of my buttocks. Some people do, and if they're comfortable, good for them. I personally don't see the need to show off these bits of my body. I'm not ashamed of them - I just live in a society where clothes are the norm and this is the way I choose to wear those clothes.
When breastfeeding, if there had been a need to have my breasts fully visible in order to feed effectively, I'd have done it without too much thought. But there wasn't, so I preferred not to. That is my choice. I'm not being suppressed by society. I'm just living in society and choosing which of the social norms I want to follow. I won't be dictated to by the rest of society if I choose to feed without covering up. Equally, I won't be dictated to by other people who think I should feed in a way that I'm less comfortable with.
Yes, if everyone stripped off on a daily basis, then we might start the process of developing a new social norm that put less emphasis on covering up, but it's not going to happen any time soon.
Yes, every woman should feel comfortable feeding her baby anywhere they choose - I fed walking about in a supermarket, in my office, while pushing DS1 on the swings etc - but new motherhood is an emotional and difficult time for many women. In lots of ways, a new nursing mother is probably the last person who should be expected to be a crusader for women's rights. She's got enough on her plate.
The world isn't going to change overnight. And no-one is going to change it by making women even more uncertain about what they can do without criticism from one group of observers or another.
Perhaps if everyone spent more time thinking about how to support new mothers in the choices they are comfortable with, we'd start moving towards being a society where women can be happy feeding covered up or entirely topless, as they choose. Instead of feeling sad that someone has chosen to cover up, why not smile at them and make them feel proud of what they're doing?
Or if defeating the social norm is more important than a mother feeling comfortable, take your own top off and start a campaign.