I love the poem but probably disagree with the sentiment somewhat. Although, I have felt like this at times.
The fact is, we will never know why we're here or if there is any reason at all to it. The only thing we can be sure of is death, absolutely. But none of that gives us an excuse to give in or not do our best to enjoy the time we're here. After all, there is nothing to lose, as you so rightly point out. Ultimately, the choice is this: spend 80-90 years downcast and miserable at the thought of certain death or spend the same time living like there's no tomorrow...there may not be.
Well written, by the way - and I like Robert Frost too - particularly 'The Road Not Taken'.