The socialists kill indiscriminately, and the Islamists target their killings, so the Islamists may seem more dangerous. But socialism/communism killed far greater numbers of people than Islam.
At first they kill those they envy, usually on the right side of the bell curve. Pol Pot first killed all the doctors and lawyers. Most of us reading this were alive when this happened. Anyone wearing eye glasses received a death sentence. Socialists always try to kill the Pareto principle where 20% do 80% of the work, own 80% of the land, and sleep with 80% of the desirable women. The problem with that plan is no matter what the socialists try the 80/20 rule reappears. It's a rule of the universe.
Tell that to all the people who were not Moslem before Mohammed's flying monkeys burst out of the Arabian desert 1400 years ago, all those across the world, from Morocco to Indonesia, who were converted by the sword.