Both are highly radical writers that are both usually interesting, and occasionally delusional. Oddly enough, they both have the same delusion, just in mirror opposite political alignment. For Chomsky any action by US against a foreign power is an illegitimate use of force, for Horowitz, it's always the justifiable use of force for the good of democracy, the US and the country attacked.
Reality isn't anyplace near the extremes portrayed by either of these men. Both are usually right at some level, but both are masters of picking the one or two points that support them while ignoring the many against them. Of the two Horowitz tends to irritate me more though, because of his pathological inability to avoid personal attacks.
Jay