The main reason is that to give people freedom of political choice does not guarantee that they will choose wisely. Consider France in 1848, when the introduction of universal suffrage resulted in the election as president of Louis Napoleon, who three years later launched a coup d'etat, suppressed his opponents and turned himself into a dictatorial emperor. Or consider the way that Hitler forced his way to power partly by means of free elections in Weimar Germany.
In today's Russia, there is every possibility that voters will turn to Gennady Zyuganov, the Communist challenger to President Boris Yeltsin. It will be a tragedy for Russia, and a serious setback to the West, if they do. Mr Zyuganov is not like the former Communists running Hungary or Poland, whose opportunistic transformation into Western European-style social democrats required a commitment to civil liberties and a free enterprise economy.
On the contrary, Mr Zyuganov and his associates reek with nostalgia for the Soviet Union and most of its works: the centralised economy, the instinct to strike hard at domestic political opponents, the pursuit of a Russian nationalist agenda cloaked in internationalist ideals. Should he defeat Mr Yeltsin in the expected second round run-off in early July, Mr Zyuganov would probably not return Russia to its blackest authoritarian past. But the fragile democratic institutions set up in the 1990s would almost certainly not be able to take the strain of a Communist presidency, and there is a serious risk that Russia's relations with the West would descend into confrontation.
As Western governments and most Russian liberals have recognised, the dangers associated with a Zyuganov presidency are so great that a Yeltsin victory is preferable. Yet a second term in office for Mr Yeltsin would bring its own problems, in Russia and outside. Neither in the West nor at home is Mr Yeltsin recognised any longer as the courageous crusader for democracy and human rights who did more than any other person to bring down Communism in 1991.
His record has been badly tainted by the brutal and unnecessary military crackdown in Chechnya. In many people's eyes, he was also wrong to blow up the Russian parliament in 1993 and introduce a constitution that hobbled the legislature and placed all effective power with the presidency - that is to say, himself. Since his first election victory in June 1991, Russia has evolved under Mr Yeltsin's leadership into a strange hybrid of democracy and autocracy. It has given ordinary Russians more freedom than perhaps at any time in their history, but it has also conferred too much power on unaccountable institutions such as the armed forces and the renamed but not so reformed KGB. Lack of proper legislative oversight has enabled sinister individuals in the presidential entourage, notably Mr Yeltsin's personal bodyguard, Alexander Korzhakov, to acquire excessive influence.
Mr Yeltsin's campaign tactics are also open to criticism. By forcing Russia's central bank to hand over 5 trillion roubles (pounds 600m) for the funding of his spending promises, the president has compromised the bank's independence - a fundamental feature of Russia's economic reform programme, on which co-operation with the International Monetary Fund and other Western institutions must depend. Mr Yeltsin's team has also succeeded in slanting television coverage of the election grossly in favour of the president, to the point where Mr Zyuganov might use Mr Yeltsin's abuse of media freedom to justify a crackdown on the Russian press and broadcasters if the Communists should win.
In his foreign policy, Mr Yeltsin has fallen short of Western expectations. He has manipulated ethnic and territorial disputes and exerted Russian economic power to regain influence over many former Soviet republics. He has strenuously resisted Nato's enlargement, without showing much sensitivity to the craving for security that dominates the attitudes of central and eastern European countries.
Still, matters would probably be worse under Mr Zyuganov. The difficult but often constructive relationship that the West has with Mr Yeltsin's Russia would turn into something more tense with Mr Zyuganov in the Kremlin. The semi-democratic, semi-authoritarian Yeltsin-led state would lose many of its democratic features under a Zyuganov presidency.
However, if the West is right to hope for a Yeltsin victory, it must also hope that there will be more progress during Mr Yeltsin's second term towards consolidating democratic institutions and making Russia a law-based state. Having suffered centuries of autocratic rule and 70 years of violence and intolerance under Communism, Russia cannot be expected to turn into a model democracy overnight. But Mr Yeltsin has, over the past three years, done as much to hinder his country's democratic development as he has done to promote it. If he wins a second term, he must use it to consolidate and extend democracy. The cause of freedom in Russia matters profoundly to all of us outside its borders, as well as within; if Russia fails, following this election, to strengthen and improve its nascent democracy, we will all suffer the consequences.