Should rational people volunteer for the military?

How do you reconcile the concept of the inalienable rights to life, liberty and the pursuit of happiness with volunteering for the military, a profession that requires obeying the orders of others -- especially when those orders may very well get you killed? If you still had the right to pursue your happiness, you could decline an unpleasant or dangerous order since inalienable implies you still retained your rights -- even after consenting to serve. But that's not how the military works -- or could work.