The point is to suppose that if Calvinism is false that the ramifications could be quite sever. Some Calvinistic believers throughout history have used their understanding of soteriology as an excuse not to evangelize. Some have allowed their view to turn "hyper" and prevent their involvement in missions. Granted, that is not what true "Calvinism" teaches, but that doesn't negate this historical fact about what SOME believers have done.
Additionally, supposing Calvinism is false, think of all the time, energy, effort and Christian resources wasted on the proclamation of its claims by its adherents and the rebuttal of those claims by its opponents. If "Arminianism" is false, no such eternal effect can be claimed...after all we are just doing as we are decreed to do, right? :saint:
But just because there are extremists, why do you paint everyone with the same brush? I also know those believers who are just stinking lazy and too embarrassed to tell others about Christ.
As for your second point, if those who disagree with the doctrine of grace would just shut up, then there would have to be no time spent rebutting them.