More wine is ruined by being too warm than too cold. A wine that is served cool can be warmed:
the atmosphere of the room, and even the drinker's hands cupped round the glass, will rapidly heat it. A wine which is warm when poured is hard to chill, and it may well have passed the point of pleasure.
In general, white wines should be served cooler than reds. But there is a sliding scale between the two, not a step. The rubric 'white wines at refrigerator temperature, red wines at room temperature" is only partly true. Different styles of white wine demand different serving temperatures, and many, if not most, reds are best served cooler than the dining room's ambient temperature.
The idea of "room temperature" dates from when our ancestors dined in what to us would be cold rooms. Wine would be stored in a cellar (which was colder still), so it made sense to bring it into the dining room in advance to let it emerge from its deep cellar chill. Today our wine storage may be at the right temperature to serve red wines, and allowing them to warm up to the centrally heated pitch of the dining room or kitchen does them harm, not good.
It is possible, even amusing, to use a thermometer to tell exactly when a wine has reached the recommended level. On the other hand, a degree or two either way will not ruin the pleasure of the wine, while the fuss with the thermometer may well spoil your evening. Use a thermometer a few times to get used to how a bottle at, say, 10°C (50°F ) feels to the touch. Then put the thermometer away and rely on your own senses.
Why do wines taste better at different temperatures? Warmth allows aroma compounds to volatilize, which is a complex way of saying that the wine's pleasant bouquet is given a chance to emerge. Different wines have different mixtures of compounds, and so give of their best at varying temperatures. This is most applicable to red wines, but complex white wines should not be served too cold because what makes them interesting - the tastes and aromas of quality and maturity - will be more apparent when they are warmer.
The reason white wines should be cold is to do with acidity. Warmth accentuates acidity, making some white wines taste harsh. When cool, this acidity allies with the fruity freshness of the wine to become appetizing and refreshing. Expectations have their influence, too: whites are expected to taste refreshingly chilly, so they should be.