There are a few problems with using your local cemetery as a yardstick for measuring mortality rates, Colin. The sample draw from the headstones is not really representative even of the bodies buried there - it is not uncommon (even now) for a great many graves to go unmarked, or to have flimsy, impermanant markers. This was particularly true of those who could not afford a more substantial marker. If you were wealthier, and happened to be among those who lived a longer life, chances were better that your life was more likely to be commemorated in this way. These visible monuments are just the tip of the iceberg, so to speak!
Rather than relying on an unreliable visual survey like this, you may want to look to studies that incorporate data drawn from registries, parish and medical records, etc.
According to studies by AmeriStat, for example, life expectancy increased significantly between 1900 and 2000 in the USA: from 51 to 80 for females, and 48 to 74 for males. There have been tremendous strides made in combatting infant mortality, and in diseases like smallpox and polio. This is not to say that we don't have the introduction and/or spread of other illnesses - AIDS, for example - but very few statiticians would dispute the general world trend towards longer lifespans.
As I said before, having a realistic view of the past does not preclude admiring the achievements of our ancestors, or believing that everything is necessarily 'better' now (the assessing of which involves subjective interpretation as well as objective data anyway). There are certain things I believe we've lost along the way that I wish we had kept. But eras build upon the achievements of those that went before - sometimes we do take regressive steps, but overall it has been an evolution. We wouldn't be where we are today if not for their achievements, but then that era didn't emerge fully formed from a clamshell either - it was a progression of what went before. The period you outline was one of great achievement and progress...sometimes. Sometimes it was one of narrow bigotry, oppression, war, famine, tragedy and death. Just like what went before and what came afterwards.
As Dickens wrote in 'A Tale of Two Cities':
IT WAS the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity, it was the season of Light, it was the season of Darkness, it was the spring of hope, it was the winter of despair, we had everything before us, we had nothing before us, we were all going direct to Heaven, we were all going direct the other way- in short, the period was so far like the present period, that some of its noisiest authorities insisted on its being received, for good or for evil, in the superlative degree of comparison only.