Experience always starts at losing that's why it's better for me to see newbies having a tough run while they progress.
I agree with your points of view. Mistakes improve a man's knowledge and experience. It is important to learn from your mistake and if you make the same mistake simultaneously then you are not concentrating. Every time a trader makes a mistake a short note about it should be taken so that he can improve his strategy by finding out the reason behind that bad trade.
Mistakes are very essential in learning, this is the only to get understanding of things very fast. But in trading I don't think it is proper for beginners to learn everything they needs to know through Mistakes. Beginners needs to put effort in learning to minimize mistakes they will come across in trading. Too much mistakes causes lose of money in trading, if their are much learning habits it will reduce the rate at which beginners lose in trading.
In trading no doubt we need experience to make things easy as we proceed in trading but we should not have a mindset that every understanding must come as a result of mistake.