When you "compete" by working in a way that damages the worker's health, yes, that should be outlawed. (Negative externalities are the fancy economics term)

Large corporations are already legalised collusion. Allowing those with competing interests to "collude" at the same level is a necessary counterbalance to that.

I'm not saying anything about that. What I'm saying is a decent amount of tradesmen don't know what they are worth and undercharge. In most instances it's because they underestimate the scope of the job they're taking on and are eager to get business. But business is generally easy to get in non-recession times and they could bid higher and still win jobs. It's often inexperienced guys and it's why you see so many startup construction/trade companies go out of business quickly. There's business - they just don't know how to run one.