In a democracy all votes should be equal.
One person, one vote is often a rallying cry for democracy activists. Everyone should have representation. But should everyone have equal representation? It would seem obvious that everyone should have the same say. Equality should be sacrosanct in a democracy should it not? There are however reasons why unequal votes may be necessary. The United States has unequal votes as a result of history so that all the thirteen colonies would sign up to the union each gained equal representation in the senate regardless of population. It is often politically expedient to give minorities a greater share of the vote than they would under one person one vote as a balance on dominance by the majority group. Inequality between votes may also not be built into the system but a result of the balance of parties within the system. A very few voters in first past the post systems have a disproportionate influence due to being swing voters in swing constituencies. So should democracies stick the the principle that everyone should have equal weight or compromise if for politics.
Equality and Univeral Suffrage
Granting the vote to all citizens (universal suffrage) was considered to be a step forward in democracies, including the UK, New Zealand, America, Australia, Denmark and Finland. This was done based on the idea that as women were not so different to men as to be unable to choose their own leaders, they should also get the vote.
Therefore, the idea is that every individual is capable of making such decisions, and must have the right to do so. To state that (for example) blacks should have less votes than whites would be to perpetuate inequality on morally shady grounds.
Therefore, the proposition argues that everybody should have the right to vote in a democracy.
Since all voters are not equal in their natural state, they must be equalized by administering lower/higher value to different votes.
Once again, this goes against the tenets of democracy. Equality for all is part of the consideration of a democracy. This is simply not achievable when certain groups have more or less political power than others.
First Past The Post
Secondly, prisoners are excluded because they have broken the law. Similarly, children are excluded because they are too join. The proposition accepts that there are certain reasons to reasonably exclude someone from the voting process - breaking laws is arguably one of these reasons.
Thirdly, whether it is practised or not does not make it the correct action. Torture is practiced in many countries, but is still considered to be immoral.