If you feel strong enough emotionally to tackle strangers over what you think is wrong with their behaviour, you need to be strong enough emotionally to accept the more than likely hostile reaction you are going to provoke.
If - as seems to be the case - you lack the emotional strength to deal with the reactions you create, the best option is simply not to create them.
No-one likes to be told by a total stranger that their behaviour is not acceptable - it may be, but that does not increase the chances of a conversation opened with criticism of a stranger ending well.
I would dial down your social conscience, and learn to accept that some people do not behave as you, or probably I, think they should, but that does not give you the right to call them out for it. They will not for one moment stop to consider the validity of your point, you will simply receive varying degrees of hostility, and it's clear you are not up for dealing with that.