Hydrogen is a nightmare to work with, and store. Other high energy-density chemicals tend to be complex hydrocarbons... So you're still burning oil - it just happens to be made from coal, or algae slush, or whatnot.
Algae slush is carbon coming from our current system, our current atmosphere, it is renewable. Fossil fuel is releasing carbon from and external source (external on a human timescale at least). It will be essential in creating a renewable replacement for oil.
Burning hydrocarbons is not the issue. Burning hydrocarbons that were extracted from the atmosphere millions of years ago, is.
Burning hydrocarbons is not the issue. Burning hydrocarbons that were extracted from the atmosphere millions of years ago, is.