Richard, what you write here is more correct than you may appreciate. While most mutations, including insertions, are neutral, some can harbor latent tragedy.
Somatic cells accumulate mutations as they divide, and they are a number of ways that insertions can happen. Infections are one such means; this is well established by real time observation both for individual somatic genomes and germ line populations.
Given that we are not so young anymore, we both are likely to possess cells which feature several insertions.