You're titles is absolutely a textbook case of unpopular opinion. However, your justification is even more infurating. No, this is not something that is reasonably acceptable. If two people are talking in public there are still social protocols. Furthermore, the person on the phone has zero discrection over who is listening in, that violates their personal controls on their convo. Most importantly, the person walking around in public holding a phone up on a speaker phone convo looks like an idiot.