Haiti's problem is corruption. Wealthy landowners farm the land with no regard to the long-term consequences. The government is totally "up for sale". The Dominican Republic had a Marxist regime until it was overthrown by a CIA backed coup under Nixon. They then adopted a free-market capitalist democracy and they are now one of the most prosperous nations in the region (I believe only the Cayman Islands, the Bahamas and the USVI are better off). Haiti and the DR share the same island with similar terrain and natural resources. The Dominican Republic is proof that capitalism and democracy is the surest path to prosperity and peace and they accomplished it in a very short period of time.
http://www.freerepublic.com/focus/f-news/1095370/posts
Although come to think of it, the example you cite about the success of the Dominican Republic may undermine some of the arguments in this article.