What makes atherosclerosis dangerous?

The end result. Atherosclerosis is a progressive disease that involves all the arterial systems of the body, the brain, the heart, the kidneys, the gut and the limbs. As it progresses, it causes reduction of blood flow to these areas chronically, and the end organ becomes a target for embolization of the plaque or blood clot caused by atherosclerosis on an acute basis.
Loss/↓ Blood Supply. Disease is an accumulation of white blood cells in the wall of arteries, body wide, in response to which the artery walls enlarge (opening remains the same) ; thus asymptomatic for decades. Rupture of the endothelial cell lining layer allows plaque to contact blood, clots form ; showers of plaque ; clots fly downstream blocking smaller arteries, stopping blood flow with resulting tissue damage.
Heart attack, stroke. It can lead to arterial blockages which can lead to heart attacks, strokes and death.