Appeal to Novelty

This is also known as Argumentum ad novitatem.

This is the fallacy in which one argues that a secondary claim Q is true simply because the subject of the first claim P is new or modern.

Normally P and Q refer to the same or related subject matter.

Examples

Social networking websites are new therefore they must be good, useful, or safe.

Immigrants being new ideas, therefore they must be good for society. (In fact, they sometimes bring old medieval and backwards thinking which is toxic to modern society.)

Some COVID booster vaccine is new therefore it is beneficial, even if it causes secondary health problems, including allegedly death.

The third sequel to XYZ movie just came out, therefore we should spend $10 per ticket to watch it.

The new king is 15 years old, therefore he is better than his dead father who was 45.

Weaknesses

Whether something is new or modern often bears no connection to superiority, despite some cultures' obsessions with newness.

Whether a new or old thing is superior has to be determined based on a full analysis of its merits, not merely on its newness.

• Nazism was once new. Its previous newness was not proof that it was better any other political ideology.
• Tobacco was once new. Its previous newness was not proof that is was better than having healthy lungs, skin, cardiovascular system, and a lack of addiction.
• The Bubonic plague was once new. Its previous newness was not a proof that it was safe or good.
• Et cetera.

It's not hard to attack a premature overestimation of the merits of a new or modern thing, when that claim is based solely on newness.

Ignorance is bliss, but knowledge is sobering.

Similarly it's not hard to spot a premature underestimation of things that are not new.