Comparisons aren't equations

Just inching its way into my top 20 pet peeves is the inability of the mainstream media (and many in the greater public) to understand that mere comparisons aren't equations.
Granted, on the surface this probably seems like petty semantics--and maybe it is--but I think far too many legitimate arguments are squashed with one sentence: "You can't compared _________ to ________!"
Yes you can.
Recently Bill O'Reilly, Fox News' bombastic cash cow in primetime, compared David Brock's Media Matters organization to Fidel Castro's communist regime in Cuba--which, of course, has a news coloring/suppressing propensity.
MM is not the mass media watchdog it claims to be because it is staked to a leftist agenda.
Point taken.
There is nothing intrinsically wrong with using comparisions to make a point.
For instance, comparing Saddam Hussein to Adolf Hitler is not intellectually dishonest; they, of course, were both tyrants in their own way. Equating the two, however, belies and understanding of history. Equating the two would be intellectually dishonest, to be sure, especially if the equation serves a malevolent end as it did in the run-up to the Iraq War.