I myself have that reaction. A couple of years ago, I had a bicycle accident and came fairly close to being run over by a pickup truck. As I lay on the asphalt, eye level with a tire tread, I was genuinely surprised at how happy I was not to have been run over, and to have escaped unscathed (give or take a bruised rib and skinned knuckles).
Looked at as a whole, however, the notion that life is essentially good is hard to justify, given the likelihood of pain and suffering and the inevitability of eventual annihilation. It's a grim fate to be a creature designed and built to desire life, yet to know with utter certainty that the universe that created you will rub you out in a few short years:
Vanity of vanities, says the Preacher, vanity of vanities! All is vanity. What does man gain by all the toil at which he toils under the sun? A generation goes, and a generation comes, but the earth remains forever. ... All things are full of weariness; a man cannot utter it.We never win; we just delay losing long enough to produce the next generation, which delays losing long enough to produce the next generation, and so on.
So do I believe that existence is bad? Of late, I'm more inclined to the view that it's meaningless to call existence as such either good or bad. Consider: Isn't it meaningless to call temperature, as opposed to a particular temperature, hot or cold?
While we exist, our instincts paint the world around us with a range of values, including the supposed value of life itself. When we're cheerful and healthy, the world seems good; when we're morbid, it seems bad. But the seeming is in us, not in the world, as are the inferences we draw. When we are not, the seeming is not: Nonexistence includes (so to speak) the absence of any perceiving subject.
Existence isn't good or bad, but to the extent our wayward feelings and thoughts permit, it contains goodness and badness and everything in between.