My first Italian professor said "amare" was only used for passionate love (couples), thus you wouldn't say it about cats. Anyone have insight into this?
Not really, although that's a good rule of thumb as it isn't used for emphasis as it is in English (e.g. "I love your hairstyle", for that "adorare" is more common). It can express any form of love, included a stronger form of like.
So, to make this clearer, based also on another experienced speaker's post, "adorare" is more common for non-romantic love.
It depends on the kind of love :) "Adorare" is mainly used for emphasis, while for a parental love it could be "amare" or "volere bene". "Amare" isn't as omnipresent as "aimer" in French, but it could also work for a strong preference, i.e. a stronger "like". It isn't easy to draw a line :)
For those who can read it, here is an Italian blog post by a language/linguistics blogger discussing whether it is possible to 'amare' cats (among other things). http://blog.terminologiaetc.it/2013/08/06/differenze-love-amare/
why do you use an article in this kind of sentence (I also saw it in "lei ama il caffe")?
The article is needed in a number of instances in Italian, much more than in English; at http://italian.about.com/od/grammar/a/italian-definite-articles.htm (the paragraph "Usage of the Italian Definite Article") there is a good explanation, together with many cases when the article must be omitted. There are many cases not covered though. In this case you're saying you love cats (or she loves coffee) as a general category, so the article is needed.
In Italian as in Spanish the use of articles is in many instances, essential. In this particular case "Amo gatti" "Amo gatos", even when they will understand you, the sentences sound incomplete.
Sono allergico ai gatti ;-) (or allergica if the speaker is a female)
I almost threw up having to fictitiously admit to this... Non amo i gatti.
How could someone not love cats? They're so fuzzy and sweet and cute and loving and adorable...