"I feel the same, there is no other profession that we all use and then club together or individually buy gifts. If I was given and received gifts in my profession I would be breaking the law. Teachers know what they are getting into when the train to become teachers."
You don't have to justify it or get cross with us teachers. If you don't want to, just don't. Nobody will mind.
But there aren't many professions where a member of your family is in contact with them, six hours a day, five days a week.
If your teacher does the bare minimum, what she's contracted and paid to do, fair enough. But if she goes 'over and above' or makes a big difference to your child, or spends her own money making the year extra special, then it's just nice to say thank you isn't it.
I have family members who work in care, and one who is a cleaner, and they are often thanked or bought chocolates or something at Christmas. It's not just teachers. I think it's jobs where you recognise that the extra effort, provided voluntarily not contractually, has made a difference to you.