If KDE or Emacs depend on a bug in the kernel, they need to be fixed. In
those cases it's actually relatively easy, since the bug has already been
triaged and the components that need fixing have been identified.
Whether or not the kernel should keep compatibility (i.e. the fix for the
regressions) is a different question. If two widely used applications show
problems with a new kernel version, then there's a non-zero chance other
applications are "broken" as well. This $unknown needs to be offset with
the cost of maintaining the incorrect behaviour.
This again has little to do with personal issues, which play an important
role in this story.