Knowing that discrimination exists while you get into something doesn't make it less discriminatory. Sure they knew what they were getting into, but I doubt they are complaining that they didn't know it was like this.
"Discrimination" is a neutral term though: there are acceptable kinds and unacceptable kinds. For instance, it is discrimination to not let a stranger sleep in your home or in your bed, though no one reasonable would call that unacceptable discrimination.
The actual policy we're talking about here is a country-neutral permanent immigration quota coupled with country-neutral per-country percentage caps. There's nothing specially discriminatory in the law against people from India. It's just that there's massive amounts of temporary-worker immigration from there, which crashes hard against the other quotas. If German immigration were equally massive, Germans would have the same problems Indians have now, so the problem has nothing to due with racial or ethnic discrimination.
You could also think of the quotas another way: they're protecting the ability of people from countries other than India to immigrate, so the incoming immigrant stream is more diverse.