Why are my commands applying to everyone instead of just the person with the tag?

Question

The commands are applying to everyone in the server (every entity on the first one) and not just the person with the tag, these are the commands in the tick.mcfunction file:

execute as @e at @e if entity @s[tag=glasswalker] run setblock ~ ~-1 ~ glass 
execute as @a if entity @s[nbt={Inventory:[{id:"minecraft:diamond",tag:{display:{Name:'{"text":"these are my diamonds"}'}}}]}] run kill
execute as @a at @a if entity @s[tag=earthmage] run setblock ^ ^ ^10 dirt
execute as @a at @a if entity @s[tag=firemage] run setblock ~ ~ ~ fire 
execute as @a at @a if entity @s[tag=firemage] run effect give @s fire_resistance 5 
execute as @a at @a if entity @s[tag=watermage] run fill ~ ~ ~ ~ ~1 ~ water
execute as @a at @a if entity @s[tag=watermage] run effect give @s water_breathing 5 
execute as @a at @a if entity @s[tag=deletion] run clone ^ ^ ^10 ^ ^ ^ ^ ^ ^ replace move 

I have no idea how to fix this.

Answer 1

You are overcomplicating your commands so much that this is causing them to fail.

Your overcomplicated version:	Simpler and works:
execute as @e at @e if entity @s[tag=glasswalker] run …	execute as @e[tag=glasswalker] at @s run …
execute as @a at @a if entity @s[tag=earthmage] run …	execute as @a[tag=earthmage] at @s run …

… and so on.

As for the second command, which doesn't match the style of the commands I showed in the table, there is a different problem—you are testing for custom item names. This is bad practice and should be avoided. See my other question for why and how to fix it.