I'm not sure that "positive" is the right word here. Biases seem to be frequently double-edged at a minimum.
The negative consequence is more obvious in your basketball example. Picking blacks for a basketball team simply because they are black is not positive. It is part of a system of thinking, which says that "blacks are good at these things". The corollary is that "blacks are not good at these other things". So, even what you might consider a "positive" bias has a reinforcing effect on the way we classify people and form other biases that are objectively and obviously negative in socially significant ways.
Likewise, classifying Asians as good mathemeticians is part of a system of thinking that says they are less good at other things. All of these preconceived notions have some value attached to them which, collectively, have a direct bearing on social status.
In short, biases tend to have a profound negative side even, or especially, when we are unaware of as much and/or believe they are OK.
The negative consequence is more obvious in your basketball example. Picking blacks for a basketball team simply because they are black is not positive. It is part of a system of thinking, which says that "blacks are good at these things". The corollary is that "blacks are not good at these other things". So, even what you might consider a "positive" bias has a reinforcing effect on the way we classify people and form other biases that are objectively and obviously negative in socially significant ways.
Likewise, classifying Asians as good mathemeticians is part of a system of thinking that says they are less good at other things. All of these preconceived notions have some value attached to them which, collectively, have a direct bearing on social status.
In short, biases tend to have a profound negative side even, or especially, when we are unaware of as much and/or believe they are OK.