In the sentence:
I used to hurt people.
to hurt is an infinitive. I read somewhere that infinitives are not verbs. So can used to be a verb? If not, should we treat used to as one entity which describes the past and take hurt as a verb?
In your sentence, 'used to' is used as a modal verb. Check OALD.
As 'used to' itself show that something happened continuously or frequently in the past, hurt is a transitive verb here.
So, IMO, in your sentence 'hurt' is not an infinitive, but verb.
Hope this will help.
The main misconception here is that a verb and an infinitive are mutually exclusive. According to LDOCE definition an infinitive is:
the basic form of a verb, used with 'to' in English
In addition to this definition, when to is omitted we get a bare infinitive.
So, in your example both used to and hurt are verbs, but in different forms.
we should treat used to as one entity which describes the past and take hurt as a verb.
Moreover, from Macmillan Dictionary: