Is there something wrong with assuming everything has a purpose.

I believe there is. It's false.

It's a good assumption, in fact, I daresay it's an assumption you should make, even if it leads to nothing. Assuming there is a purpose for something, a reason for things, or a good solid answer to the why question... really does push inquiry. We learn a lot about physics when we ask "why the sky is blue", we learn a lot about biology when we ask "why plants are green". Why does pollen on water jiggle? Why do we always see the same face of the moon?

The problem with the question is, it's not actually true. Aristotle once wrote "Nature does nothing uselessly." -- strictly speaking, this is completely false... nature does everything uselessly. Purpose has no bearing on evolution. However, when we look at things in nature it's extremely useful to ascribe purposes to things. Hands are for holding. Teeth are for chewing. Legs are for running. Eyes are for seeing. Wings are for flying. If we look at it, the way nature actually works: those organisms with those traits survived better to build and expand upon their successful strategies. That's helpful in some ways, but the lie is seemingly more useful. When we look at the universe as being filled with purpose, we can say to ourselves, "Oh, wings are for flying... so when I build this airplane, I should build wings on it."

This way of thinking is useful, but not true. When we look on something and ask, "Why does the sun revolve around the Earth?" or "Why do we have an appendix?" or "What was before the Big Bang?" -- We don't have answers. But, people are inclined to shove a God-of-the-Gaps into these problems. This doesn't provide any utility to a person, and the only reason we assumed there was a purpose to things was because it's a very useful thing to assume. So basically, we're assuming there is an answer, and then shoving in a worthless answer to stop the inquiry. You might as well not ask the question, if you aren't going to honestly seek the answer.