Atheism doesn't entail secular humanism, but I think the optimistic atheists who do believe not in inevitable progress but in the nobility of the attempt to at least incrementally advance socially and technologically vastly outnumber the nihilistic atheists who think all hope is lost without God.

Secular humanism is a pretty broad category that isn't the same as political liberalism or socialism, although I think it's closer to the political left than to the right. At a minimum, secular humanism would be just the view that human nature isn't execrable, so there's a chance we deserve some respect even without the supernatural rationale for our projects.