If you are a science major you are likely to enter graduate school. If you are fascinated by science and love to understand the world around you, you will try to make the academic experience last as long as possible. Hence you will consider doing a PhD. You may even see yourself capable of being part of the big machinary of scientific research for ever. Thus, after the PhD you will likely end up postdocing. In itself, it is not a bad thing. I have only one word of warning: a bit of postdocing is good, too much postdocing (ie more than 2 positions, up to a total of 4 years) is a bad thing. This is just my personal opinion based on my own experience, hence the opinion is based on n=1.
Three reasons why too much postdocing is bad:
1) The pool of candidates you would compete for a permanent job increases with every year you spend in a postdoc position.
2) Do not illude yourself: there are not that many permanent jobs in academia so the sooner you join the non-academic market the better.
3) Like anyone else, scientists age. It is best to leave the academic bubble before one is too old and therefore not so easily employable/retrainable.