Efforts have been put for electronization of complementary currencies (alternative forms of monetary media) in the hope that it would reduce their operational cost. However, this paper argues that the problem is more inherent in the core design of MCS[7] (Mutual Credit System), the most common form of complementary currency today. By simulating a small world of 2,500 traders, we show that growing the number of free-riders in MCS has a paradoxical effect of increasing "welfare" (a "happiness" metric) of the community. Since there is no pressure to stop the growth of the bad users, it is difficult to sustain the soundness of the system without strong interventions from the operators of the system; we need alternatives to the alternatives. We have proposed i-WAT[6] as an electronic descendant of the WAT System[10], a polycentric complementary currency using "WAT tickets" as its media of exchange. A simulation using the same model as above indicates that i-WAT users can sustain barter relationships even in the presence of free-riders by natural evasive actions to avoid risks.