- to concentrate power and wealth in the few, and,
- to distribute and dilute responsibility among the many.
When an autocratic or a monarchic tyrant does evil, his tyranny is plain. When a democratic ruler does so, it can remain hidden and be justified as the will of the people for a much longer period.
Monarchs and dictators, whose actions are evil, are overthrown by revolt and revolution and this threat is a real check on their evil intentions, not to mention a competition for the setup of government. A democracy on the other hand, seemingly, introduces competition in governance by lowering the barrier to entry. However, this is superficial. Democracy replaces the real fear of revolution with the innocuous "If you don't like 'em, just join 'em".
Further, in a democracy, the government is a mere care-taker. Care-takers of property, normally, make shorter term decisions with sub optimal economic consequences as compared to owners.
Power corrupts. Absolute power corrupts absolutely. Even absolute democratic power.
The only alternative is the dissolution of statist power and the restoration of individual liberty.