The disadvantage of a one-party system is that it does not tolerate opposition. In such a system, only one political party is allowed to exist, and this party exercises complete control over the government and all aspects of the society. Since there is no competition from other parties, there is no need for the ruling party to consider or respond to the opinions or concerns of the people.
This lack of opposition means that the ruling party can impose its policies and agendas without challenge or accountability, which can lead to corruption, abuse of power, and suppression of individual rights and freedoms. Furthermore, the absence of periodic elections means that there is no opportunity for citizens to express their opinions or to vote for alternative candidates or parties, which can further entrench the ruling party in power and reduce the possibility of change or reform.