Missing link is not a scientific term. Given the preponderance of ancient life forms that have been found as fossils that are clearly transitional between the major classes of animals and plants today, arguing against evolution is not even tenable.
Experiments with unicellular or multicellular organisms have so far provided no evidence of any directionality in evolution. If such evidence comes up, the theory of how genetic variations occur will be adjusted accordingly. Its highly unlikely at this point as stochastic models does such a great job of replicating how mutations actually occur in genes. The observed fact that most mutations are neutral or harmful also tells the researchers that mutations have no inbuilt directionality. All directionality comes from the subsequent selection process among the variant descendants.
Since there exists many unicellular life forms that are very very simple and from which more complex life is clearly descendant from (from both fossil evidence and genetic and protein tree analysis), we know that life has increased its structural and functional complexity many folds over the eons, and evolution is the perfect process that can do this job.
Honestly, if I were to scrutinize this at level that creationism is scrutinized, I could, rather easily, show how this is somewhat to mostly nonsensical. I mean, we could just start with this referencing a quote where the words "missing link" are nowhere to be found. Answering to that and then the little side debate one could have for that could be short lived or 18 more pages of thread discussion. The rest of what is being said here, some of which includes terms that are not 'scientific' would allow for a field day, if you know, all we are bringing to the table is scrutiny and deeming that good / righteous debate strategy.