The point is the principle that that they feel they have the right to decide whether man should interact with the opposite sex and fornicate freely or not, how to we regulate the rules and laws that Man determines etc. The fundamental principle here being that man possesses the right to legislate and make rules and laws.
Practically individuals are appointed in Parliaments and legislative houses to debate, scrutinise and enact law. The basis of legislation is the majority decision of these selected people, who will vote according to their own personal experiences, their party line, their business interests (More often than not) and the like. This is something that is contradictory to the very foundations of Islam and its basic beliefs i.e. that Allah is the sovereign master and the only one with the right of determining legislation and rules and laws as He pleases and the rest of creation including mankind had no right except to Hear and Obey the orders of Allah. So Islam and Democracy Contradicts with each other and Islam has its own Political System.