Why Aren't Political Assassinations More Common?

This heavily overlaps my answer to this question at Politics.SE, but I am not indenting this self-quotation for ease of reading.

Given the presence of internet, good encryption, and digital cash, why hasn't "assasination politics" taken off?

The main reason that this doesn't happen is that participants in the political process and business leaders who want to influence politics are more dentological (i.e. they make ethical decisions on a rules based basis) and less utilitarian (i.e. they make decisions considering only the pros and cons of conduct on a probability weighted basis) and less cynical (i.e. caring only about their own self-interests) than we give them credit for being.

But there is wide consensus among political players that assassination isn't an acceptable political tactic, so this option isn't even "on the table" for consideration from the people who would order hits in developed countries.

There are places, such as societies where organized crime plays a pervasive role (e.g. the so called "narco-states" like Ecuador, Mexico, and not so long ago, Columbia, and much earlier, mafia controlled Southern Italy), or where totalitarian regimes consider this an acceptable tactic (see, e.g., Putin's Russia or China) where assassination or extra-legal execution is common place.

The ability to anonymously retain hit men isn't the limiting factor that is preventing assassination politics in places where assassinations are currently rare (although the recent example, of a non-political hit in a professional dispute that was the cause of lengthy litigation that got subcontracted several times in China before everyone involved was caught illustrates the role these technologies can play in hired killing outside of politics).

It is already overwhelming true, and has been true for a long time, that the political end of removing a politician or judge from the "political field" in developed nations through political violence is far cheaper and easier in raw dollars and technological capacity, than it is to achieve the same ends through lawful legal and political means. A skilled sniper paid tens of thousands of U.S. dollars worth of untraceable cash or precious metals or gemstones can kill an individual target at a distance of many hundreds of yards with only a modest risk of being caught in the act.

Digital cash and crypto-currencies address an issue that hasn't historically been a problem. There have been lots of ways to untraceably transfer value with plain old paper cash or valuable objects for literally thousands of years. Before there was the Internet, there were anonymous snail mail drops and trustworthy brokers between people who want to carry out hits and people who are willing to carry them out. Codes sufficiently good to not be deciphered by authorities seeking to solve assassinations likewise date back, at least, to the Greco-Roman classical era, if not earlier.

The term "assassin" itself dates to the use of the term to refer to members of the Nizari branch of Ismaili Muslims at the time of the Crusades, when the newly established sect ruled part of northern Persia (1094–1256 CE) and sought to kill what they saw as illegitimate European invaders and conquerors (and their perceived allies).

Ultimately, politics is about co-opting the power of government and the law to achieve your ends. Achieving political power through assassination may allow you to win that zero-sum game of short term battles for control of the law making and enforcing apparatus. But in doing so, you undermine the authority and value of being able to control what laws are made by undermining the ability of the state to secure compliance with the law.

So, if you are a politician, or a big business person, your interest in having people obey that laws that you as a member of the establishment can influence to some degree makes the policy of obeying the laws prohibiting political murders more important to you than the gains you could achieve by violating those laws yourself, even if the risk that you will be caught is modest.

If you open the floodgates to widespread use of political assassination as a political tactic, eventually, you may be assassinated. Equally important, the vitality of a strong state with a strong rule of law that you would hope to control would be undermined.

Also, in most democracies, there are relatively few political figures who, if assassinated, wouldn't be replaced by someone advancing similar policies in short order. So, in a lot of political systems, political assassinations of a great many potential targets only provide a modest and short-term benefit, to the person doing so. A political assassination only makes "rational" sense (1) if the person assassinated is firmly entrenched so that they cannot be removed by other means, and if the replacement for that person in the political system would be very different on the issues important to the person commissioning the assassin, or (2) if the purpose of the assassination is more to intimidate promising people supporting some cause you are opposed to from participating in politics entirely, than to remove the particular person assassinated from power.

Who actually uses assassination and other forms of violence as a tactic?

Criminal gangs, Appalachian families in blood feuds with each other, and lower working class men in legal disputes with each other, all of whom are particularly ill-equipped to achieve their desired ends in through the legal system.

The use of assassination as a tactic is tied to weak states, to cultures of honor that arise in weak states, to regimes that have significant numbers of subjects who view them as illegitimate, and to situations where some form of corruption or lack of democracy or current or imminent permanent minority status for the people using that means is perceived as making non-violent means of securing political gain utterly futile.

Assassination and other forms of political violence are tactics people use when there seems to be no other viable option to achieve their needs which they perceive as intensely urgent, or when the targets of the assassination are so dehumanized that the rule against assassination no longer seems to apply to them.

Another way to think about it is that political violence is a form of asymmetric warfare that occurs when people reach a point of declaring war to achieve their ends. The decision to cross this threshold is justified in much the same way that decisions to declare war generally are justified.

The same factors that drive the decision to use political assassination as a tactic or not, also drive the openness, for example, of the American far-right, to using the rhetoric of political violence, something that is on the rise in the U.S. These advocates perceive that they are on the brink of losing cultural and political hegemony to people with values whom they view as completely unacceptable in a non-negotiable manner, and that neither the political institutions in the U.S. nor its courts provide them with a way to preserve a way of life that they seek to maintain, so they are willing to consider violent alternatives to the non-violent political and legal process to continue to remain in power.