So if you say that someone has narrow ambition it can mean that they have a very restrictive focus on their goals and may not achieve them because of this close minded approach. It can also describe someone who is extremely focused on one area, for example a brain surgeon may have his ambition described as narrow. So in these examples it can have both a negative and positive connotation. Blind ambition does have a negative connotation because it describes someone who has a disregard for his well being, or the well being of others in the pursuit of his goals; They use the concept of "The end justifies the means". We use the word blind in association with many negative emotions such as blind rage, blind lust and even its derivative blinding fury.

Negative: it is ambition for its own sake, which doesn't care what harm it may do.

It's a negative comment. It is saying something like, the person took little into account and did not look at at the effect of his want to achieve his goal.