This sounds very strange to me given the fact that by definition a monopoly is the control of a market by one entity, it doesn't have anything to do with how it gets there.
Having a monopoly is not illegal. Abusing that monopoly to gain unfair advantage in another market is illegal. People use the term "monopoly" to interchangeably mean "legal monopoly" and "illegal monopoly", which does get confusing.
Well that depends on the country. In some countries monopolies are illegal and the government is the only one that can perform ones.
Also, questionable practices are not necessarily illegal. For instance, no that long ago (well 20 years or so is not that long for me), having privileged information on wall street wasn't illegal, but questionable.