Most people who choose not to vote aren't being systematically repressed. They're just too indifferent and/or lazy to participate.
No, it doesn't. It lowers the threshold for dictating policy, and biases it to particular interests; that makes tyranny of those interests more likely, including when they command a bare majority (or even large minority) of support.
You don't fight tyranny of the majority by unequal representation; you fight tyranny of the majority with constitutional limits on what government can do at all, or by requirements for supermajorities or (as some state constitutions do) multiple time-separated votes (or both!) for particular kinds of action.
Crafting campaign finance laws in such a way that those with more wealth can disproportionally affect election outcomes is anti-democratic.
Voter suppression/disenfranchisement in the form of impediments to voter registration, voter ID laws, felon disenfranchisement, misinformation about voting process/procedures, closure of DMV offices, etc. are all anti-democratic tactics used by political parties to reduce/refuse voting access by constituents.
If a party can make voting inconvenient/inaccessible to a targeted population they can win electoral outcomes that do not match constituency desires.
Voter suppression is real. Voter suppression works.