The prohibition on Birthdays serves several purposes.
1 to restrict worldly association
2To make witnesses seperate from those around them
3To provide a talking point about the religion
Probably many more. To address the witness issue that birthdays make people think too much of themselves, if you consider it rationally you only get 1 birthday a year where you are the centre of attention but you have many opportunities to show generosity to others on their birthdays. It says in Acts that there is more happiness in giving than receiving but the scripture doesn't suggest you never receive, merely that generosity is a joy. It is important to learn to give with no expectation of receiving birthdays are a chance to learn this important lesson.
I once did a talk on Birthdays setting a school teacher asking to celebrate my sons forthcoming birthday in circle time. I went through the examples and then got the householder to say. That is all very interesting but I wasn't planning to sacrifice anyone during circle time. I think I may have been exiting mentally at that stage but no one noticed.