> You buy icecream for your kid and not for the random kid.

discrimination is about rules not about individual actions.

It would be "everyone can eat ice cream", or "ice cream is unhealthy and no one can eat ice cream".

If the rule is "Ice cream has too much sugar and because of the obesity epidemic we decided to ban ice cream, except for my son who is super special boy and he can have it every day" that is discriminatory. Even if your son doesn't eat it and effectively the rule is the same for everyone in practice.

On the basis of "resources are limited" you end up with discussions of rights that are equal on paper but discriminatory in practice. "Everyone can buy a house", but some people are rich and some have nothing. You have freedom and equality but also homeless people.

Here the question however is about in groups and out groups. So its for example about "theft is wrong" where you only arrest people stealing from supermarkets but not the CEO of the supermarket when he is stealing people salaries with mandatory unpaid overtime.

That is a law where rich people are covered by the law (their business is protected) but they are exempt (their theft is unprosecuted). That is the kind of in gorup/ out group being debated

Yeah, if you restrict the meaning of "discrimination" and "ingroup" and "outgroup" to examples making your point obvious and true then it's obvious and true.