Debemos is the 1st person plural form of deber in the present tense.
In this sentence, it most naturally means we must or we should, with a strong sense of moral obligation.
Because Spanish often uses the definite article with abstract nouns when speaking about them in a general sense.
So:
In English, we often leave the article out with abstract nouns, but Spanish frequently keeps it.
That is why contra el odio sounds natural, while contra odio would sound incomplete or wrong here.
Yes, absolutely. That is also natural Spanish.
Both mean something like We have to / must fight hatred, but there can be a slight nuance:
In many contexts, though, they are very close.
Because in Spanish, only two common contractions happen:
But:
So:
A simple pronunciation guide is:
deh-BEH-mos loo-CHAR KON-tra el OH-dyo
A more Spain-focused IPA version is:
[deˈβemos luˈtʃaɾ ˈkontɾa eˈloðjo]
A few useful notes:
No. Luchar is very natural, but other verbs are possible depending on the tone:
Luchar contra is especially common when talking about social problems, injustice, discrimination, and similar ideas, so it fits this sentence very well.