BNP debate on Question Time

Personally I don't see why people are so concerned about this, what are they frightened of.
If the BNP are as bad as they are made out to be then having them involved in debate on Question time can only be a good thing.
"Give them enough rope and they will hang themselves" I think is the expression.
We must however preserve the right that we all have of Freedom of Speech as stifling debate is always a bad thing and just narrows peoples opinions thus fuelling extremist causes.