It's interesting the reaction when people witness nature in the raw be it crows or magpies, sparrowhawks, grey squirrels or cats and yes they do all consume songbirds, chicks and eggs but nature is nearly always in balance and in modern history at least, it is only man's predation, not that of other animals, that causes extinction. If there wasn't predation by other birds and mammals then my guess is we would be overrun with certain species of songbirds many of which would starve to death due to limited food supplies.
One aspect that always seems to be overlooked when it comes to the slaughter of songbirds and that is the volume killed every year by cars. Outside my cottage in the last fortnight, three housesparrows - severaly depleted in numbers in recent years - have been left squashed in the road by vehicles that have no interest in eating their prey. When I walk along country lanes, I come across countless corpses of wrens, blackbirds, goldfinches and the like, not to mention toads in the spring and hedgehogs in the summer. And imagine how many more badgers there'd be if it wan't for the motor vehicles taking out dozens every night!