We're constantly told that No Deal would be a failure of statecraft. An election on 15th October merely guarantees that failure. Allowing Boris Johnson control of the date, too, is the chief issue here. Agreeing to an early election gives him control over when to set it, and since there's very little reason to trust anything Johnson says, why take his suggestion that he'd hold it on October 15th seriously?
All of this stuff about opposition parties "running scared" is just an attempt to seize the narrative, but it's based on very little. The SNP won't be scared -- they are almost certain to crush the Tories in Scotland. The Lib Dems won't be scared, either -- even if they don't translate support into seats, they're on the up right now. And, after the events of 2017, when Corbyn was expected by more or less everybody to be utterly marmalised but somehow ended up gaining 40% of the electorate and removing May's majority, do you really think he'd be scared of the campaign either?