  The Universe is neither homogeneous nor isotropic, but it is close enough
that we can reasonably approximate it as such on suitably large scales. The
inflationary-$\Lambda$-Cold Dark Matter ($\Lambda$CDM) concordance cosmology
builds on these assumptions to describe the origin and evolution of
fluctuations. With standard assumptions about stress-energy sources, this
system is specified by just seven phenomenological parameters, whose precise
relations to underlying fundamental theories are complicated and may depend on
details of those fields. Nevertheless, it is common practice to set the
parameter that characterizes the spatial curvature, $\Omega_K$, exactly to
zero. This parameter-fixed $\Lambda$CDM is awarded distinguished status as
separate model, "flat $\Lambda$CDM.'' Ipso facto this places the onus on
proponents of "curved $\Lambda$CDM'' to present sufficient evidence that
$\Omega_K\neq0$, and is needed as a parameter. While certain inflationary model
Lagrangians, with certain values of their parameters, and certain initial
conditions, will lead to a present-day universe well-described as containing
zero curvature, this does not justify distinguishing that subset of
Lagrangians, parameters and initial conditions into a separate model. Absent
any theoretical arguments, we cannot use observations that suggest small
$\Omega_K$ to enforce $\Omega_K=0$. Our track record in picking inflationary
models and their parameters a priori makes such a choice dubious, and concerns
about tensions in cosmological parameters and large-angle
cosmic-microwave-background anomalies strengthens arguments against this
choice. We argue that $\Omega_K$ must not be set to zero, and that $\Lambda$CDM
remains a phenomenological model with at least 7 parameters.
