It is not by design, it is a known weakness. The intent behind the actions also matters and it would be known to the malicious miner that to take these coins fr

It is not by design, it is a known weakness. The intent behind the actions also matters and it would be known to the malicious miner that to take these coins from exchanges would result in a loss to the exchange. So it would be illegal. If however the miner maintained 51% + network share and then wrote some code to create new coins and adopted that code and mined blocks awarding himself 1000 coins for each block, he could legitimately do that and then sell those coins. Of course this could lead to the price dropping as soon as people realised what was happening and likely to happen before the attacker could send enough coins to an exchange to make the same sort of profit as in the situation in the article.