"Prosperity is the best protector of principle" taken out of context can be used in many ways, including by a rich person arguing that rich people have better morals, and poor people have worse ones, and that's why they're poor.
Whether one is trying to use it literally or ironically, it means the exact same thing. The only question is whether the speaker and the reader understand what it means. And in fact in this case there was no context at all in Twain's original usage - it was the epigraph for a chapter in this work. [1]
And that's what I mean in that modern writing, on the internet - though rapidly leaking into 'real life', has become highly infantilized where we assume everybody reading is an idiot, and speak accordingly which, in turn, infantilizes and 'idiotizes' our own speech, and simply makes it far more bland and less expressive.
Interestingly, this is not ubiquitous. In other cultures, including on the internet, there remains much more use of irony, and more general nuance in speech. I suspect a big part of the death of English fluency was driven by political correctness - zomg what if somebody interprets what I'm saying the wrong way!?!
The context is really necessary.