The first page of the diary of Columbus of his first voyage of discovery. After reading it you can see why the left hates Columbus:

"IN THE NAME OF OUR LORD JESUS CHRIST

Whereas, Most Christian, High, Excellent, and Powerful Princes, King and Queen of Spain and of the Islands of the Sea, our Sovereigns, this present year 1492, after your Highnesses had terminated the war with the Moors reigning in Europe, the same having been brought to an end in the great city of Granada, where on the second day of January, this present year, I saw the royal banners of your Highnesses planted by force of arms upon the towers of the Alhambra, which is the fortress of that city, and saw the Moorish king come out at the gate of the city and kiss the hands of your Highnesses, and of the Prince my Sovereign; and in the present month, in consequence of the information which I had given your Highnesses respecting the countries of India and of a Prince, called Great Can, which in our language signifies King of Kings, how, at many times he, and his predecessors had sent to Rome soliciting instructors who might teach him our holy faith, and the holy Father had never granted his request, whereby great numbers of people were lost, believing in idolatry and doctrines of perdition. 

Your Highnesses, as Catholic Christians, and princes who love and promote the holy Christian faith, and are enemies of the doctrine of Mahomet, and of all idolatry and heresy, determined to send me, Christopher Columbus, to the above-mentioned countries of India, to see the said princes, people, and territories, and to learn their disposition and the proper method of converting them to our holy faith; and furthermore directed that I should not proceed by land to the East, as is customary, but by a Westerly route, in which direction we have hitherto no certain evidence that any one has gone. So after having expelled the Jєωs from your dominions, your Highnesses, in the same month of January, ordered me to proceed with a sufficient armament to the said regions of India, and for that purpose granted me great favors, and ennobled me that thenceforth I might call myself Don, and be High Admiral of the Sea, and perpetual Viceroy and Governor in all the islands and continents which I might discover and acquire, or which may hereafter he discovered and acquired in the ocean; and that this dignity should be inherited by my eldest son, and thus descend from degree to degree forever. Hereupon I left the city of Granada, on Saturday, the twelfth day of May, 1492, and proceeded to Palos, a seaport, where I armed three vessels, very fit for such an enterprise, and having provided myself with abundance of stores and seamen, I set sail from the port, on Friday, the third of August, half an hour before sunrise, and steered for the Canary Islands of your Highnesses which are in the said ocean, thence to take my departure and proceed till I arrived at the Indies, and perform the embassy of your Highnesses to the Princes there, and discharge the orders given me. For this purpose I determined to keep an account of the voyage, and to write down punctually every thing we performed or saw from day to day, as will hereafter appear. Moreover, Sovereign Princes, besides describing every night the occurrences of the day, and every day those of the preceding night, I intend to draw up a nautical chart, which shall contain the several parts of the ocean and land in their proper situations; and also to compose a book to represent the whole by picture with latitudes and longitudes, on all which accounts it behooves me to abstain from my sleep, and make many trials in navigation, which things will demand much labor."

Thank you, Matthew. To me, Columbus was essentially just the name of the man who “discovered America”.  This really helps to fill out the picture.

Also, you bolded words are noted.

Columbus was a great man and is worthy of our celebration and remembrance.

And that's why they despise him.
As a fellow one of Italian descent and the nation that employed him, I am proud of Cristoforo Colombo.