There are surprising pieces of information we learn about God and the way He views certain types of people and their actions.

For thou art not a God that hath pleasure in wickedness: neither shall evil dwell with thee.

The foolish shall not stand in thy sight: thou hatest all workers of iniquity.

These statements from Psalm 5:4-5 (KJV), tell us something extremely important about God. At first glance, it may appear that the statements only tell us that God hates sinners in general, but a closer look tells us that this isn't the case. If it was the case, then the phrase, "thou hatest all workers of iniquity" would apply to the Psalmist himself and us.

The phrase "workers of iniquity" really gives the sense of those people who have abandoned all righteousness and dedicated themselves to all things evil. These are not the people who sin from time to time (or the average sinner), but people who have deliberately chosen sinful ways as a lifestyle and revel in it. The Psalmist is describing people who have literally given themselves over to evil, to partner with evil, to allow themselves to be a conduit for all manner of evil thoughts, words, and deeds.

Commentator Adam Clarke makes this statement in reference to this phrase.

Some sin now and then, others generally; some constantly, and some labour (sic) in it with all their might. These are the WORKERS of iniquity. Such even the God of infinite love and mercy hates. Alas! what a portion have the workers of iniquity! the hatred of God Almighty! [1]

I like the way he explained it. Workers of iniquity are laborers in evil and direct all their energy to that end from waking to going to sleep. A good picture develops for us with that description.

John Gill goes says it slightly differently.

...such who give themselves up to work wickedness, who make it the business of their lives, and are slaves unto it, living in a continued series and course of impiety; and this character does not only belong to openly profane sinners, but to some professors of religion; see Matthew 7:22; and these are the objects of God's hatred. [2]

So it becomes clear that God hates that type of person because they enveloped with evil, to be fully utilized of and by it. They live only to be consumed by evil itself and willingly commit themselves to every evil practice continually, deliberately choosing that path.