There is nothing wrong with marble floors. The things I would consider are the vulnerability of marble when it comes to kitchen spills and utensil drops. Marble is soft as stone goes and is in some cases damaged by such things as acid from juices and stains from grease and some liquids. I think it is a bad choice for a kitchen.
In an entry it also has some vulnerabilities when it comes to footwear coming from the outside scratching the floor stone. Today's footwear can easily collect and hold small stones that can cause great damage to a marble floor when walking on it.
In the interior of a home in a bathroom marble would be fine. Not much footwear in a bathroom usually and few things in a bathroom can stain the marble.
To say it is a "no-no" isn't correct. Yes, marble has been used for thousands of years. Hell take a look at Washington D.C. Keeping in mind marble that is inches thick like that used on building exteriors and underfoot is a lot different than the highly polished marble floor tiles offered today.