In "The Sick Rose," love isn't what we expect it to be; it's not that timeless, cohesive force that other poets, movies, and books always talk about. It's "dark" and "secret" and doesn't really do anything good for the rose; it's almost like a disease that infects the rose and destroys it. Love definitely isn't all you need in this poem.
The kind of love described in the poem is bad because it is "dark" and "secret." The poem suggests that love should be public, or at least not secret.
Love isn't what we normally think of as love; it means something more like sex, which suggests that the speaker of the poem is viewing the situation from a flawed perspective.