Why would government observers complain that the filibuster allows a minority to control the senate?

The filibuster is the right to unlimited debate a bill.

This leads to the abbility of the minorities to do an ever debating process con a bill they don´t feel like passing. Though this could be used wrong, it also assures that every bill that passes is well thought and well discussed. THe large parties with majority at senate have considered in the past making a move on removing the filibuster with no success yet.