First -- Just because we're better than we were 30 years ago does not mean we're good. A huge chunk of the world is still in poverty, and we have the capability to eliminate that completely but we don't use it. We still have climate change, overfishing, et cetera wrecking long-term environmental havoc that won't be fixed by simply decreasing our CO2 output. The middle east is still a bloodbath and it doesn't look like that will end any time soon. Workers around the world, even in America in some places, are being exploited as much as they were in the 20s. So no, it doesn't seem to me that the world is just peachy right now.
Second -- I can't speak for liberals, but we on the far left are still fervently optimistic. We're seeing all this shit going on around us, and we still think we can make it better if we try hard enough. However, the writer of this article seems to define 'optimism' as 'faith that everything is all right'. In that sense, no, we're just about as pessimistic as can be, and we've been pessimistic since the 19th century. All the problems we have today are fixable, but most require radical solutions that 'optimists' like the author of this article would probably shy away from.