HogansHero said: A text is a non-verbal telephonic communication. Analyze it as if it had been verbal.
It's a little bit splitting hairs, but I think overhearing a phone call and looking at someone's phone screen long enough to transcribe an entire email require significantly different degrees of effort, and I think they have different expectations of privacy.
If I had a phone call on a plane, I would expect everyone within a 5-10 foot range to hear it whether they wanted to or not. If I typed an email on a plane, my expectation, assuming the decency of the people around me, would be that no one would see it unless they intentionally chose to do so.
In any event, when I say invasion of privacy, I don't mean in a strictly legal sense. I know people's texts in public aren't legally protected. I mean people - right or wrong - have an expectation that their texts, even if done in public, will not be read by others. And if someone makes an effort to do so, that would be an invasion of that expectation of privacy. Earlier in the thread I described it as "unethical" and "questionable". It's also "rude", if that helps you understand.
I also think it's bad precedent. This time everyone is like "oh, it's fine, he was supporting a monster" but the next person whose private emails are exposed might have their life ruined for doing something you agree with. What was considered horrible 50 years ago? What about 50 years from now? It's important to be careful what norms we create, because they could just as easily be used against you one day.