I do this a lot myself.

The following is not a rationalization. It is reality: other people are kinda horrible. They're horrible enough to deserve having expectations of mistrust. This is either overt (passive-aggression, pettiness, malice, etc) or from bad habits (laziness, flakiness, selfishness, etc). The net result is people are not dependable. Your brain is not "jumping to conclusions" to hurt you. These shortcuts are constructs, reinforced through complex feedback loops, to help you. Your brain evolved over millions of years to help you understand and process (as quickly and accurately as possible) the world, not make you feel guilty. Keep this in mind.

You *want* to trust people and that's cool. In some respects, it makes life easier.

...but if you mistrust these people, perhaps it's your brain tipping you off to find more trustworthy people. It's better to not get twisted up in an effort to rewire millions of years of evolution and just admit that you're surround by (attracted to?) bad people and you should stop doing that.