WHY?

Why did/do Communist countries seal their border to keep their own people in? If Communism is as great as the Liberals in the West claim, why are communists ready to kill their own people, to prevent them from leaving? Mexico and other non-Communist poor countries assist their unemployed or criminal citizens in leaving, to remove the economic burden of those people from the govt. operating budgets, and I can understand that, it makes sense, but how do you explain the tendency of Liberals/Leftists/Socialists/Communist/Democrats to force others to accept their beliefs and/or policies, even if they themselves don't actually practice what they preach? If their ways are so good, and so effective, shouldn't they simply embrace them, knowing that others will come to see how right they were, and in turn embrace them willingly? Taxes, public schools, union shops, public medicine, "clean/green energy", redistribution of wealth, you name it, they want the govt. to impose them all on the population, but they themselves don't just lead by example. Joe Blow's auto body shop can be shut down, or regulated out of profitability, in the name of "clean air", but Hollywood, whose product requires countless amounts of energy/pollution to deliver is overlooked. Why? Is it because Hollywood largely embraces the Left? I can't modify the exhaust on my Harley, but Gore, Bono and Oprah can dump tons of carbon and decibels into the atmosphere, and that's all cool with Sacramento and DC? WTF?