We may feel sympathy when we read about people killed for protesting in Syria, Bahrain, Libya, and other countries.  But tyranny isn't just something happening to unfortunate people somewhere else.  It's an existential risk to human civilization.

Civilization - even tribalism - relies on altruism.  Altruism is defined as cooperation that is not the happy convergence of interests of rational self-interested agents.  That happens too; but we don't call it altruism.  Altruism is, roughly, helping others without the expectation of reciprocation or cooperation.  And it happens because humans like helping other humans.

Altruism is probably mostly genetic.  It's an evolutionary adaptation that instills the desire to help others into a species.  Social pressure can install some amount of altruism; but it's my opinion that this would not work at all without a pre-existing genetic basis.  Many species exhibit altruism to a level at least as great as that in humans.  Some insects, which are incapable of feeling social pressure, are far more altruistic than humans.

Two theories for how this happens are kin selection and group selection.  Regardless of which of these you prefer, both of them have two important weaknesses:

• They are both very weak effects compared to selection for traits that benefit their organism directly.
• They require special social conditions, on society size (on the order of 10 members per society in the case of kin selection) and immigration/emigration rate (extremely low in both cases).

It's not known whether humans are still evolving, or have begun devolving due to lack of selective pressure.  But in the case of altruism, we can be sure:  Even if some selective pressure still exists, most humans today do not live under the necessary conditions for either kin selection or group selection.  Humans are living off their evolutionary capital of altruism.

Tyranny, whether it's that of Syria, Iran, North Korea, Nazi Germany, or the Soviet bloc under Stalin, aggressively selects against altruism.  The most-altruistic people were among the first executed in all those places.  They are the people being shot while protesting in Syria.  Social activism under such a government is rarely in your best self-interest.  Tyranny selects for self-interest; people who are willing to help the state oppress others are given opportunities for advancement.  And it removes altruistic genes quickly from the population, likely undoing hundreds of years of evolution every year.  Those genes will never be replaced.

I'm not too worried when this occurs over a few short months or years.  But when a people lives under these conditions for generations, you may end up with a large population deficient in altruistic genes.

There's no solution at that point short of gene therapy.  The population can stay in place, resulting in a society that is at best hopelessly mired in corruption and poverty, and at worst a danger to the rest of the world.  Or it can disperse, and dilute altruistic genes around the globe.

ADDED:  Knowing whether this is a real problem or not, would require learning something about how many genes are involved in altruism, and what their distribution in the population is.  A legitimate objection to what I wrote is that if genes for altruism are distributed so that killing less than 1% of the population would have a major impact on their abundance, then they probably weren't very important to begin with.  Although, sociopaths are only around 1% of the population, and they have a major impact on society.  I wonder how much work has been done in studying the maintenance of alleles for which you only need a few members of the population to have them?