I did mean greatest in the sense of best and most desirable. It's a weakness, but NOT a flaw. Every design or form has weaknesses, things that can break it. Compassion is one of ours, but it's critical to the survival of our species and expression of our nature.
Edit because I apparently jacked up the quote box code.
So compassion is Humanity's crumple zone? I can live with that analogy.
I don't know if I'd put it that way, really. Compassion is kind of the thing that makes us work as a species; the ability to connect with and care for other people is inherently crucial to everything we consider uniquely human achievements. Only a social species can develop culture and technology, and the biological, developmental condition on which sociability is dependent is compassion.
In my experience, compassion is also the only thing that makes us work as individuals too. Whatever form that may take.
TWJ: It's not a weakness (even when making the distinction of weakness from flaw), it is in the make up of the canvas on which we paint the parts of our inner lives that we feel raise us from 'mere animals'. It's part of what makes us 'other'. It's one of the reasons why even the most evil of people don't believe they're evil.