In Colombia lots of terrible things have happened. There is people that had made a fortune simply murdering and stealing entire families, and of course drugs.
Peace process means legalization of all this crimes, and laundering all the money and power gotten mainly by extortion. There are thousands of victim's families that are angry because it means no justice for them, the people that killed their family members will not go to jail and the properties that were stolen will not go back to the families.
Uribe put the guerrilla on his knees by force, making it to want to make a deal in the same way the Germans or Japanese wanted a honorable peace deal when everything was lost. Now Santos gets all the Glory basically capitulating against the Guerrilla.
The deal is a very bad deal, for example it makes Guerrilla a "democratic" party, but if the people do not vote them, it does not matter because representation is warranted by law, basically giving them the territories that they already controlled by force.