Legally, it's easy. But getting the HR bureaucracy to go along with it is a long and unpleasant process. The last time I fired someone for doing no work at all and arguing over everything, it took about 8 months.
Unfortunately, my company is not unusual in this respect.
There are a lot of companies without HR. Due to my background I haven't been hired for for a company with an HR (other than contract work) for probably a decade. If you want to hire and fire people easily, look for small companies, usually less than 20 people. Beyond that the CEOs tend to get tired of dealing with human administrative tasks, so it gets offloaded to HR. CEOs have a lot more risk tolerance so naturally when HR gets involved they focus on saving their own asses (which usually means taking low-risk rather than highest profit) rather than the good of the company.
Unfortunately, my company is not unusual in this respect.