Answer:
It is necessary to be critical of elected officials (in a democratic system) so as to let them know when they are not doing a good job. This criticism can come in form of peaceful protests, use of pressure groups (these are people that come together to try and influence a government decision to their advantage), or simply voting the elected officials out in the next election.
This is important because the electorates (the people that are eligible to vote in an election) are the ones that hold the power and the elected officials are expected to serve the people.
Suppressing objective critiques is dangerous for democracy because it turns a democratic system to an autocratic one because in a democratic system, everybody, including the elected officials and electorates are subject to the rule of law and must be held accountable. One of the ways of being held accountable is by criticizing objectively whenever an elected official does not perform his duties well.