By delegating to a validator, a user delegates staking power. The more staking power a validator has, the more weight it has in the consensus and governance processes. This does not mean that the validator has custody of its delegators’ Atoms. By no means can a validator run away with its delegator’s funds.
Even though delegated funds cannot be stolen by their validators, delegators are still liable if their validators misbehave. In such case, each delegators’ stake will be partially slashed in proportion to their relative stake.