In the popular culture, Intelligent Design is often portrayed as trying to be an alternate theory to evolution. However, as the following question points out, it is not scientific, and so cannot be an alternative theory.
But, this also puts evolution in a tight spot. Science progresses by competing theories. Yet, there is no competing theory to evolution as a whole, only variations within the theory (e.g. Neo-Darwinism vs Punctuated Equilibrium). So, if there are no scientific alternatives to evolution, does that make it unscientific as well? If there are no proposed alternatives, how do we know evolution got it right? And finally, what would a non-ID alternative to evolution look like?
Full disclosure: I am quite interested in ID, and do believe it is scientific and testable, but that is not what I am addressing with this question.
UPDATE: For those downvoting this question, how do you suggest I improve it? Is it not a valid question?
To use an evolutionary analogy, without a diversity of theories our understanding of where we came from will not evolve and remain fit. Shouldn't evolutionary theory apply to evolutionary theory itself?