I like that tumblr has a “heart”, not a “like” button.
When I heart a post, it doesn’t mean I necessarily like what it’s saying. A lot of posts are about bad things happening, they’re heart-rending. When I click that heart, what I’m saying is that the post is touching me in some way. I may actually like it, I may be laughing along with you, it may mean that you’ve made me think in a new way, I may be feeling friendship, or compassion, it may even mean that you’ve triggered lust, or desire. In some cases it even means that I’m feeling anger, or sorrow, because of a post.
In the end, it boils down to this: You’ve touched my heart. And therefore the symbolism in the act is perfect.