I hate this day, it doesn't make sense at all.
Same like Christmas. It's a commercial party to keep you trapped in the matrix.
For Christians it is a celebration for the birth of Jesus Christ.
Oh cmon, Jesus wasnt even born on that day. There's no historical documented evidence to support it. The Roman Papacy just drew a lottery and chose a random date to use as another weapon to enslave humanity in the chains of religious dogma.
Your first sentence is correct. Based on historical documents it's estimated that Jesus was born in summer, not in winter.
It is celebrated in winter because of economical reasons and I don't like this either.
But if Jesus' birthday would be celebrated in summer, it would be fairly close to the celebration of his resurrection, so it kind of balances both celebrations.