Christians sometimes feel or say that they ought to suppose other people have 'good intentions', and that this attitude is entailed by being loving, as we are required to be.
But this is a mistake. Christians simply need to judge the intentions of others as accurately as possible, and then act accordingly.
When a person is judged as having evil intentions, then this may need to be said explicitly; and such a person should be treated as such.
The Christian injunction to love, and not to hate - comes-in in the sense that a person's evil intentions should not be taken as a justification for hating them; because such emotions as hatred, resentment, grudge-bearing, vengefulness are un-Christian.
Of course, most people cannot help but feel hatred, resentment, cannot help bearing grudges, cannot stop a desire for revenge. However, such feelings should be acknowledged to be wrong, should be repented, and should not be justified.
As Christians, we must acknowledge that we ought to be able (were we perfect in our obedience) to love even those who are motivated by evil - as did Christ.
But that does not-at-all mean we should always assume good intentions, nor that we should always give people 'the benefit of the doubt'. To do that would be dishonest (a sin) as well as simply foolish.
Christians are not supposed to be self-deluding dupes, deranged by wishful-thinking - but to be clear-eyed realists.