Ambition is a double-edged trait, where too little will get you nowhere, and too much can be just as bad.
Having high ambitions is not wrong and in fact, most people who are greatly successful, become so, only because they've dared to dream big. Being ambitious is not wrong, as it's the first step to success and it leads us to work towards what we want.
Then, being consumed by your ambition, and diving head first, without any preparation can be foolish. Ambition is good, agreed, but it should be complemented by planning and perseverance.
Being born in a small town, that was simply too small for my dreams, and becoming some would argue, "overly ambitious," and driven, I've experienced ambition on both levels. Growing up in a small town, my ambitions were often discouraged and I dealt with others trying to crush my dreams. Thankfully, for me, being told I couldn't do something, gave me more strength to find a way to do it. Over time, you learn there will always be others who intend to dissuade you from success and you learn to use your own discernment to size up their motives and essentially be your own lookout.
Ambition is what pushes us to achieve our dreams, the reason we are motivated to get out of bed in the morning, and the driving force propelling us toward that fire inside us fueling us to fulfill a purposeful life, and driving us to make and reach goals.
Without ambition, there would be no advancement in any field of study, no personal accomplishments, and certainly no purposeful life to live. Ambition is a great contributor to society, and necessary for a fulfilling and accomplished life. Additionally, ambition is important, as it breeds innovation and we would never innovate unless we aspired toward something greater.
The problem with ambition, is simply how one defines it. Some assume that ambition entails devaluing other parts of our lives, which is not accurate, as ambition goes hand-in-hand with many other factors. Ambition is simply striving for something greater that what you have.
Some are instantly intimated by ambition, due to complacency, and sadly, those who are complacent simply do not have that fire within them, that desire, to strive for something better, and accept change to allow it to happen.
All in all, ambition is outlining a workable goal, usually long term, and taking measurable steps to reach that goal. Having ambition is not negative - one much work towards what they want, strive to get it, and learn what it means to earn it.