Calvinist Greg Welty states: Clearly then, the controversy between Calvinists and non-Calvinists over unconditional election is not the Calvinists’ assertion that God elects some for salvation, since non-Calvinists believe this too. Rather, the controversy is over the Calvinists’ negative claim, namely, the denial that divine election unto salvation is on the basis of works or foreseen faith. (link) It's interesting to me that while Calvinists are not united on the doctrine of election; they all agree Arminianism is wrong. So as opposed to formulating the doctrine of election in a positive assertion unique to Calvinism, they simply deny the Arminian view of foreseen faith. This has it's roots in the supra vs. sub lapsarian controversy. If they all agreed that God choose from among pre-fallen man or post-fallen man they could form such a positive assertion. But since they disagree on this point, they go with the enemy of my enemy approach and target Arminianism.
The problem is this "raises the bar". Calvinists must now shoulder the difficult task of proving a negative – they must specifically take out Arminianism. So instead of showing XYZ is taught in scripture (or the preponderance of evidence leans that way), which is all the Arminian must do; Calvinist must show ABC is denied in scripture (not just ‘not taught’, but explicitly denied). In short, internal disagreements within Calvinism require them to shoulder an a-symmetrical burden of proof in comparison to Arminianism.