All that can come of it are germs, crying, and the exploitation of the child as a political prop. But there's a way to end the madness.
While vying for the presidency, Andrew Jackson once visited a town where, "according to a campaign tale, a proud mother handed a dirty-faced baby up for him to hold." Paul F. Boller recounts what happened next in his book Presidential Campaigns:
"Here is a beautiful specimen of young American childhood," said Jackson obligingly. "Note the brightness of that eye, the great strength of those limbs, and the sweetness of those lips." Then he handed the baby to his friend John Eaton.
"Kiss him, Eaton," he cried, and walked away.
This is supposedly the first documented instance of a politician being handed a baby to kiss. I suspect the practice dates back even farther. What is certain is that it has happened enough in the years since that it's now a cliche. Life magazine explained the phenomenon in its July 4, 1960 issue: "There is only one excuse for baby kissing: it works. The aim, whether the pol is a machine-backed hack or a machine-bucking amateur, is to win the votes." So it goes today. It works to hold babies, so politicians regularly do it, and who can blame the for fulfilling their role?
Still. If the demand for small, cute little humans to hold is understandable, the steady supply of them is puzzling, isn't it? I'd kiss babies if I were running for office. But were I possessed of a child, as a father or even a babysitter, I'd never dream of handing my little bundle to a politician.