This is more or less the only advantage of authoritarian regimes, and one of the main reasons extremists often turn to them.

A one-party state is characterised as a state where only a single political party is authorised to represent the interests of the nation. Whilst the ideological monopoly present in a one-party state takes away the need to spend long periods of time debating conflicting ideas in order to achieve a consensus, the virtual absence of all meaningful debate in such a nation is arguably more detrimental to its advancement. Legislative chambers become “rubber-stamp” bodies which exist only as a means to implement the executive body’s policies without much thought as to their practical merits. Consequently, in countries such as North Korea and Eritrea, this has led to severe economic and social underdevelopment. Moreover, in the absence of a proactive legislative chamber, a one-party state experiences a larger, more powerful and highly-centralised bureaucracy, for example the USSR’s “nomenklatura”, a phenomenon which arguably hinders efficiency. Hence, although a one-party state’s ability to remove the prospect of potentially time-consuming and contentious debates may be considered an advantage of this arrangement, it is certainly not a significant advantage as it is greatly outweighed by the fact that meaningful debates are prevented altogether, which causes even more delay to progress in a democratic political system.

You mean like Cuba, N.Korea, Venezuela and most of the middle east? Yeah, so much for democracy.

This is a bit malformed and it's leading to a very weird split of people agreeing and disagreeing. This "opinion" isn't an opinion. It is a FACT that one party states can avoid democratically induced delays. The real question is, does this fact make a one party system worth it? The answer is NO... It would be like if someone said, "Dictatorships have the highest potential to get the most done." And that's absolutely true. Look at how much Hitler got done. What's your point?

Would there still be competition with a one-party state? If not, is that really democratic?

If it's the right party there is no need for other parties. This party would have to represents the interests of the people. So why would they go against themselves?

Government should have a mix of sides and views, or majorities and minorities in order to check and balance power.

A significant DIS-advantage of a one-party state is that it avoids all the arguments that delay 'progress' in a democratic political system.

Question is loaded. One Party systems can function extremely democratically, some moreso than the USA's elections for example.

It's a statement that is correct. Without opposition, a governing body can push through a policy very quickly. Example: I live on my own; without opposition, I can choose what is for tonights dinner in a mere second. Shepards pie. No delays, no arguements, no debates. Shepards pie. In no way am I supporting a single-party state, but I am saying that without opposition, they can get away with so much more in a shorter period of time.

Its true, but that doesn't means that a one-party state is better. This doesn't cancel out the significant downsides of a one party state. Avoiding argument is a good thing when the policy is needed immediately for emergency purposes, and bad thing at any other time.

The extreme left and the extreme right both agree with this for different reasons.