Ever heard of the economic impact of chronic disease? Its in the trillions per year (CDC, WHO, others). Ever consider the economic value of a human life? Its around $5 million. Since around 50 million people die each year from disease we can estimate the societal burden of disease to be ~$250 trillion dollars per year. If you do an full analysis, I would have a hard time believing you'd find the societal burden of terrorism is greater than the detrimental impact of disease.
US agencies place a $5-10 million value on an American life [1]. This is not the value of a life anywhere, though. For example, part of the valuation comes from discounted earnings calculations, which is lower in lower-income countries.
Furthermore, just because problem A is worse than problem B (measured in dollars) doesn't mean we should spend more money fighting problem A. Money should be spent where it has the greatest impact.
Most people don't make over $1 million dollars in a lifetime. I like to think the value comes from the desire to compensate a family member for a lost loved one. Some manner of putting a dollar value of the pain of the loss.
Also the greatest impact of spent dollars comes from investing in knowledge creation since new knowledge benefits everyone who will exist in the future, and we are extremely close (on the earth time scale) to our species becoming effectively permanent (space faring). So any minor new discovery can have enormous benefits, or at least benefits that are many orders of magnitude greater than stopping any number of different terror attacks.
You also have biological terrorism to worry about. Both natural (new severe viral outbreaks as in 1918 virus) and man made threats, which are not included in any estimates of the toll of disease.
