They originated in western India, and were eventually chased further west out of India in the 700's because everyone hated them.
During their travels, they established little shitholes throughout Iran, Turkey and south-eastern Europe.
They are "travelers", and refuse to be "bound" by a job, or by otherwise doing anything worthwhile, so they end up stealing cars and valuables, housebreaking, squatting, mugging, begging and scamming to get money.
Some of them also prostitute their children (because by the age of 16 all gypsy women look like wrinkly pieces of shit), and somehave been convicted of trafficking minors for prostitution.
In addition to being criminal scum, they're also filthy scum, and are famous for, quite literally, shitting in their own (squatted) nests. They also shit in public areas, like playgrounds, parks, and the streets, without any shame.
In Norway, several attempts have been made to give them a proper education, jobs and housing, but it always ends up the same way; they don't let their kids attend school, they refuse to work, and they end up razing the house, as they cover it in faeces and garbage, while tearing the building up to gather the copper wires in the walls.
The government also set up a bunch of public restrooms to keep them from shitting in Oslo's University Botanic Garden, and after less than a week they had already covered the insides of each toilet with shit, stolen all the toilet paper, and destroyed most of the toilets.
tl;dr: gypsies are hated everywhere because they are lazy criminal scum who smear shit on everything, and throughout their entire history, someone has always wanted to assimilate, kill or sterilize them.