But when you try to apply this concept of avoiding the extreme, you end up with a life that doesn't depict radical Christianity at all. Let's just take economics as an example. If you were to tell the early church in Acts to avoid extremes, you'd tell them not to horde their money, but also not to give their money away "unwisely." They should live modestly, but they also should make sure to save enough to put their immediate family first, to put their kids through college, and to have a safe, comfortable retirement fund to provide for their future. You certainly wouldn't tell them to share all their possessions and to give to those in need to a point that it hurts them and their families. Yet that's exactly what the early church did.
The thing is, God's commands are extreme. So hording for self and spending in excess for self both fail to demonstrate love, just in different directions. They're both egoistic. But selling possessions, giving to the poor at cost to yourself, and sharing in common are extreme measures, but they are beautiful goods. I think we have to nuance the term "extreme" or else we equivocate on it. When we say don't go to extremes, what we should mean is that we shouldn't err to either side, either extremity, or either direction. What we shouldn't mean is that we live a life devoid of actions which are extreme and powerful. Think of it like driving on the road. When you stay in the middle - in your lane - you go at high speeds and have purpose and direction. But when you go into either ditch, you hit ruts, signs, fences, guardrails, and you slow down or crash. Extreme speed can only be maintained when avoiding the extremity of the road.
Chesterton has a wonderful discussion on this in his book "Orthodoxy." Chesterton argues that Christian virtue is not the avoidance of extremes, but rather the furious joining of two extremes. Courage, for example, comes when one counts his life as lost while simultaneously desiring to preserve his life. To only count one's life as lost is to be a suicide, while to only care about the preservation of one's life is to be a coward. Courage, like most/all Christian virtues, can only be held if one holds both extremes in the middle. The Christian life is an extreme life and we ought not to use this idea of "avoiding the extreme" to water down how we are called to live.