could do without people who want to vote for policies of which they'll never see the consequences.

Incentives are never straightforward. People can vote for policies that move others' money into their pocket. People can vote for policies that they don't understand (based on either stupidity or naiveté). People can vote for policies that benefit their town to the detriment of the neighbouring one.

People can also vote for people (MPs), who later renege on their promises.

Democracy is a mess, but be careful before disenfranchising your compatriots. If you succeed with that, 10 years down the line you may find out that someone managed to turn the same weapon against you. Politics is rotten enough as it is.

how do you propose we achieve that - remove the right to vote at age 50?