Cooperation is essential for all domains of life. Ironically, it is intrinsically vulnerable to exploitation by cheats. Hence, there is an explanatory necessity that triggers a lot of evolutionary biologists to search for mechanisms that could support cooperation. In general, cooperation can emerge and be maintained when cooperators are sufficiently interacting with themself to provide a kind of assortment and reciprocity. One of the most crucial and common mechanisms to achieve that task are kin selection, spatial structure, and enforcement (punishment). Here I used agent-based simulation models to investigate these pivotal mechanisms against conditional defector strategies and concluded it could easily violate all of them and take over the population. This surprising outcome may cue us to rethink the evolution of cooperation as it illustrates that maintaining cooperation may be more difficult than previously thought. Moreover, besides the theoretical findings, there are empirical applications such as invading the cooperator population of pathogens by genetically engineered conditional defectors, which could be a potential therapy for many incurable diseases.