Learn English – Subject + combined with (make or makes ?)

The verb in a sentence may be a single lexical verb (a verb with distinct 'meaning') or a 'chain' of one or more auxiliary verbs ('helper' verbs) followed by the lexical verb.

However many verbs there are in the chain, only the first is inflected to agree with the subject of the sentence for tense, person and number. The other verbs in the chain are all "non-finite" forms: an infinitive or 'plain' form, or a present or past participle.

In your example the subject is hypocrisy, which is 3rd person singular, and there are two verbs, whose plain forms are do and make. The first verb, do, is inflected to agree with its 3d person singular subject, and the second takes its infinitive form:

Hypocrisy doesn't make you a human.

That is a singular pronoun, so it requires a singular verb—That is.

And since the pronoun what, which is the subject of MAKE, refers to that, it is also taken to be a singular entity, and therefore takes a singular verb—What makes.

Refraction of sunlight—that is what makes the beautiful rainbow.

If you are speaking of several things which make the beautiful rainbow, you must use a plural pronoun at the beginning of the sentence:

Sunlight and droplets of moisture in the air—those are what make the beautiful rainbow.