Accountability is one of the bedrocks of representative government. Its absence may indeed lead to long-term instability. An accountable political system is one in which the government is responsible to the voters to the highest degree possible. Voters should be able to influence the shape of the government, either by altering the coalition of parties in power or by throwing out of office a single party which has failed to deliver. Suitably designed electoral systems facilitate this objective.
The conventional wisdom in this area may be simplistic. Traditionally, plurality/majority systems like FPTP were seen as leading to single parties taking office, while PR systems were associated with multiparty coalitions. While the broad logic of this association remains valid, there have been sufficient examples in recent years of FPTP elections leading to multiparty cabinets (e.g. in India) or of PR elections leading to the election of a strong single-party government (e.g. in South Africa) to raise doubts about the automatic assumption that one kind of electoral system will lead to particular governance outcomes. But clearly, electoral systems do have a major impact on broader issues of governance, for both presidential and parliamentary systems.