Let Hercules himself do what he may,
The cat will mew, and dog will have his day.

And again:

Be thou as chaste as ice, as pure as snow,
Thou shalt not escape calumny.

This, it is to be feared, is merely the sad truth, for mankind, while it
admires both greatness and goodness, would seem to resent the one and
only half believe in the other. At all events, nothing is more to its
taste than the rumour that detracts from the great or sullies the good;
and so long as the rumour be entertaining, it has little concern for its
truth.

Froude, in writing of Caesar, has this to say admirably to our purpose:

In ages which we call heroic, the saint works miracles, the warrior
performs exploits beyond the strength of natural man. In ages less
visionary, which are given to ease and enjoyment, the tendency is to
bring a great man down to the common level, and to discover or
invent faults which shall show that he is or was but a little man
after all. Our vanity is soothed by evidence that those who have
eclipsed us in the race of life are no better than ourselves, or in
some respects worse than ourselves; and if to these general impulses
be added political or personal animosity, accusations of depravity
are circulated as surely about such men, and are credited as readily
as under other influences are the marvellous achievements of a Cid
or a St. Francis.