"We all live in the gutter, but there are still people who look up to the stars." It means that we all live in this seemingly cruel real society, but there are still people who have dreams.

What Wilde wants to express is hope. No matter whether you are in good times or bad times, you must have hope.

Extended information:

"We all live in the gutter, but some still look up at the stars" comes from "Lady Windermere's Fan" and appears in the third act of the play.

Reference: Lady Windermere’s Fan-Baidu Encyclopedia