This is exactly the way the establishment wants you to think - do whats in their best interests, not the voters...
So, instead, you may end up with a highly-rated televised debate between Trump and Sanders - where it elevates Sanders to the General Election stage, it potentially pits two people who will point out their differences with Clinton - and she is not there to defend herself. Sanders is in a no-lose situation here. If he performs well, he gets an opportunity to sway super delegates who are worried about the Clinton baggage.
What Clinton should have done was to accept the debate, schedule it for a weird time, and use it to continue her pivot to the general election - going after Trump, and ignoring Sanders.