No one is saying the Sox rolled over for Bard. It was simply a perfect storm: Bard clearly preferred to start, and the need for him to be a starter, given the state of the pitching, arised.
Also, keep in mind that the Aceves example does not apply, because had Bard completely flunked out as an SP in Spring Training, we'd probably have Aceves starting games right now. So again, it's a combination of desire from the player plus necessity from the team.
Now that Bard has been converted, it makes no sense to pull the plug on the project because Bailey got injured.