That is complete BS. Adding additional lac repressor will just repress the
T7 polymerase more. You might have a problem transforming with the lac
operator. This binding sequence may titrate out the repressor inducing the
polymerase. Even then, the cells will live fine. Even if you induce the
polymerase and have a T7 promoter with no translatable gene attached, the
cells will live fine. Lethality occurs only if you induce the T7 RNA
polymerase and have a T7 promoter transcribing a translatable gene.