When you summon Guardians with the NoAI NBT tag set to 1, you’ll receive damage through its thorns effect.
What I expected to happen was...:
The AI-less Guardian shouldn’t be able to use its thorns effect.

What actually happened was...:
The AI-less Guardian is able to damage the player using its thorns effect

Steps to Reproduce:
1. Summon a Guardian using /summon Guardian ~ ~ ~

2. Change the gamemode to survival and attack the guardian.