  We compute the $2\rightarrow 2$ gravitino scattering amplitudes at tree level
in supergravity theories where supersymmetry is spontaneously broken. In the
unitary gauge, the gravitino becomes massive (of mass $m_{3/2}$) by absorbing
the Goldstino, and the scattering amplitudes of its longitudinal polarisations
grow with energy as $\kappa^2 E^4/m_{3/2}^2$, signaling a potential breakdown
of unitarity at a scale $\Lambda^2\sim m_{3/2}/\kappa\sim M_{\mathrm{SUSY}}^2$.
As we show explicitly in the Polonyi model, this leading term is cancelled by
the contributions coming from the scalar partner of the Goldstino (sgoldstino),
restoring perturbative unitarity up to the Planck scale. This is expected since
supersymmetry is spontaneously broken, in analogy with the situation occuring
in the Standard Model, where massive gauge bosons scattering preserves
unitarity at high energy once we consider the contributions from the Higgs
boson. However, when supersymmetry is broken by the new Fayet-Iliopoulos
$D$-term, with ungauged R-symmetry, the above cancellation does not occur. In
this case, the unbroken phase is singular and there is no contribution able to
cancel the quartic divergences of the amplitudes, leading to a cutoff
$\Lambda\sim M_\mathrm{SUSY}$ where the effective theory breaks down. The same
behaviour is obtained when supersymmetry is non-linearly realised.
