Really. Without it we would be dead.
The greenhouse effect helps regulate the temperature of our planet. It is essential for life on Earth. Without it we'd all be Popsicles. The temperature of the Earth would be about 32 degrees below freezing -- zero degrees Fahrenheit!
What is the greenhouse effect? Heat from the sun is absorbed by water vapor, carbon dioxide and trace gases. These heated gases then radiate heat back to the planet's surface.
The term, "greenhouse effect" is misleading because a real greenhouse does not behave like the atmosphere. A greenhouse warms like a blanket, suppressing the exchange of air between the inside and outside. As noted, this isn't how the atmosphere keeps the Earth warm. The atmosphere doesn't suppress heat exchange, it helps it.
Our concern isn't that we have a greenhouse effect, but whether it's increasing so much that it is hurting the Earth, our only refuge in the cold universe.