Speculative essay topics about ethics or morality often generate great interest. This is especially true of subjects that are relevant to you and your peers. Items such as religious tolerance, prejudice, racism and equality offer a wide variety of areas you may explore. Consider how an issue such as religious tolerance positively or negatively affects the quality of your life or that of others. Extend this premise by addressing the ethical implications and consequences of intolerance.
Whether technology helps or hurts society as a whole is one topic you may explore with a speculative essay. What is technology and what kind of sociological role does it play? Speculate on this in terms of changes between the advent of the prehistoric wheel and a computer, or narrow the time focus. Twist this premise a bit and apply it terms of how technology affects you individually. Many experts regard the development of writing as a form of technology, too. Address how this may affect or disaffect society or even you personally.
Topics about politics or economy are ripe for a speculative essay. Decisions about how government spends money, why they spend it and the results are just three possibilities. You may write a speculative essay using fiction; for example, two imaginary characters (or two countries for that matter) sit on the opposite sides of some economic and political "table." Political theories on models of power and trust work well with this subject area.
Essays about education in some form are generally quite effective. If a teacher gives you a sentence or phrase for your speculative essay such as "the student has money," write about the status of higher education in America. Another spin on that premise might be that the student robbed someone else; you then create an essay about crime and a personal experience you had with it. Remember, keep your essay topic within range of the teacher's particular assignment.