Selfishness.

Our survival instinct tells us to hoard and be greedy so that we can survive. So while some have more than they need, others go without.

Hatred and intolerance are the most visibly dangerous qualities, but both stem from ignorance.

Dishonesty only works on the ignorant.

Complacency is not necessarily a result of ignorance, but is only harmful to oneself or others in the face of other dangerous qualities.

Love and compassion are never dangerous until they become twisted. And they cannot become twisted unless one is ignorant of the emotions.

So ignorance really is the most dangerous quality in anyone.

Human Nature itself is what causes the most suffering and hardship. There is no possible way to narrow it down to one trait.

Dishonesty. When you deal with dishonesty the result is not based on reality and so it is fatally flawed. Failure to deal with reality leads to fatalities.

I think ugliness. The uglier you are the more you suffer.

I would say cowardice.

I think it stems from laziness

If more people could be convinced that their efforts would be worthwhile, problems stemming from laziness could be mitigated.

Stubbornness.

It keeps us from getting over old ideas and accepting new ones. It prevents progress, generates war and perpetuates detrimental ideas.

Our larger-than-average buttocks.

Because having big asses enabled us to walk fully upright, which in turn left our hands free, which enabled us to pick up sticks and rocks and pummel our neighbors with them, which then in turn led to the development of more complex brains so that our neighbors could come up with a good way of pummelling us back and then we could come up with a better way of pummelling them again . . . and then keep doing that for a few thousand years 'til we get to nuclear and chemical weaponry, all because humankind's great big backsides enabled our ancestors to stand up and thwock their neighbors over the head with a tree branch.

The ass, fo shizzle.