Recently a lot of pundits have been making the point that renewed protests in Iran are unlikely to bring the government down, something with which I agree. However one reason a lot of them have been giving is that the Iranians are more willing to ruthlessly use force to stay in power, as demonstrated by the events of summer 2009.
The Iranian regime has an atrocious human rights record, let there be no doubt about that. It's a record that is in many ways worse than a lot of the pro-Western regimes in the region. But the events of 2009 do not at all point to it being more willing to kill vasts amount of people to stay in power. Stephen Walt also challenges the WSJ on this topic, but by saying that the Mubarak regime didn't brutally repress protestors "this time round" I think he misses a key point.
According to Green movement leaders themselves, 72 people died in the post-election protests in Iran (the Iranian government said around 36). That compares to at least 360 in Egypt and over 200 in Tunisia. The contrast to Tunisia is particularly strong, given that the Iranian population is around seven or eight times larger, and given also that, based on reports of the protests, vastly more people in Iran took to the streets than in Egypt or Tunisia (there were reports that one march in Tehran was three million strong alone; the Tunisian marches were tens of thousands strong and the highest estimate I heard for a Cairo demonstration was two million).
That makes the per capita death toll of demonstrators vastly higher in Egypt and Tunisia than in Iran. Based on these figures, Western-backed regimes' security forces seem to have shown far greater willingness to kill than the Basij did in 2009. Indeed one of the lessons the regime likely drew from the fall of the Shah in 1979 was that massacring people is a great way to stiffen their determination to overthrow them, something Mubarak and Ben Ali and their police forces (though possibly not their armies) seem to have missed.