When the ANC says it encourages debate and that in a healthy democracy all issues are open to debate, they obviously don't mean public debate.
The African National Congress (ANC) on Wednesday pulled out of a public debate on the protection and defence of the Constitution as it did not see the value of discussing subjects that did not pose "key institutional, policy and political challenges".

The debate, hosted by the Helen Suzman Foundation, was attended by representatives of Congress of the People (Cope), the Democratic Alliance, the Independent Democrats, the United Democratic Movement (UDM) and academics.

Notifying the foundation of the ANC's decision not to participate, spokesperson Jessie Duarte wrote that if one looked "beyond the rhetoric, objectively" there was no threat to the country's constitutional order or to the rule of law.
full story from M&G here
And then we have Jacob Zuma's reluctance to debate with Helen Zille.
Democratic Alliance leader Helen Zille has once again challenged ruling party president Jacob Zuma to a public debate.

The ANC leader called himself a "firm democrat", yet time and time again he had declined to join her and other politicians on a public platform to debate issues of national importance, she said in a statement on Wednesday.

"Zuma has ducked the opportunity to debate me on at least five occasions in 2008," she said.

Zille was responding to a remark made by Zuma during an interview with Business Day after his party's manifesto conference at the weekend.

He reportedly told the newspaper: "I am a firm democrat. There can be no issue that cannot and should not be debated."

Zille said Zuma needed to be true to his word and debate her in public.
full story from IOL here
I suppose, as the ruling party, engaging anyone in debate other than themselves is really just a waste of time. Why bother with hearing anyone else's opinion, or waste your breath justifying your own when everyone is just going to vote ANC anyway.