"To the pure, all things are pure, but to the defiled and unbelieving, nothing is pure; but both their minds and their consciences are defiled." - Titus 1:15 ESV
The statement seems to describe two kinds of people.
The naive person thinks all things are pure because their imagination can not yet fathom the depth of deception and evil in the present circumstances. It might be because of lack of exposure but it might also be the pair of rose colored glasses they wear. This person is dangerous in their simplicity.
The second type of person described is a Godly person who is well aware of evil and trouble but sees God's hand in each circumstance. The purity this person sees is not the illusion of the purity of man... it is the purity of God.
"Blessed is the man who trusts in the LORD, whose trust is the LORD. He is like a tree planted by water, that sends out its roots by the stream, and does not fear when heat comes, for its leaves remain green, and is not anxious in the year of drought, for it does not cease to bear fruit. The heart is deceitful above all things, and desperately sick; who can understand it?" - Jeremiah 17:7-9 ESV
It is amazing how those ideas mesh together in that passage. The wise person has roots that touch an underground stream. The water up on top can be quite polluted but there is water below out of sight for those that believe.
There are so many people that mean well that just have deceitful hearts. They may even want to help people but in the end the get things all twisted up because a crocked person can only get things straight by mistake.
"Trust in the LORD with all your heart, and do not lean on your own understanding. In all your ways acknowledge him, and he will make straight your paths. Be not wise in your own eyes; fear the LORD, and turn away from evil. It will be healing to your flesh and refreshment to your bones." - Proverbs 3:5-8 ESV