This is a very important essay on what metta is :
Metta is a wish for happiness — true happiness — and the Buddha says to develop this wish for ourselves and everyone else: “With metta for the entire cosmos, cultivate a limitless heart.” (Snp 1.8)
But what’s the emotional quality that goes along with that wish? Many people define it as “lovingkindness,” implying a desire to be there for other people: to cherish them, to provide them with intimacy, nurture, and protection. The idea of feeling love for everyone sounds very noble and emotionally satisfying.
But when you really stop to think about all the beings in the cosmos, there are a lot of them who — like the snake — would react to your lovingkindness with suspicion and fear. Rather than wanting your love, they would rather be left alone.
Others might try to take unfair advantage of your lovingkindness, reading it as a sign either of your weakness or of your endorsement of whatever they want to do. In none of these cases would your lovingkindness lead to anyone’s true happiness. When this is the case, you’re left wondering if the Buddha’s instructions on universal metta are really realistic or wise.