Why did Stalin physically eliminate all those dissatisfied with the Soviet regime?

Stalin was afraid of losing his power, so he tried in every possible way to strengthen it. This strengthening could be prevented by people who did not agree with his ideology and politics. Such people could prepare riots, uprisings, which would undermine the stable situation in the country. The way out of this situation was the physical destruction of dissidents. With such an approach, it was possible to cause fear in people to protest and object, thereby retaining their positions. It also helped to rally the population.