I do agree that it is a very good idea, but compulsory voting doesn't solve the corrupting effect of large districts.
The second benefit, for election integrity activists, is preventing the "under vote", where down ballot races which are left blank, and potentially filled in by helpful administrators.
Note that in the US, ballots in metro areas can easily have dozens of races. Sheriff, judges, schools, water district, city, county, state, national, referendums, levies, etc.
Mexico doesn't do too well, but apparently mandatory voting isn't enforced.
Radicals like me believe no taxation without representation. I support enfranchising pretty much everyone, especially for local issues.
It is an interesting question if the vote should be extended to non-citizens. I can see good and bad aspects to doing so and I am not sure which is more important.
For reasons of equality among the states, the US capital is not located in any of them. The District of Columbia, not being a state, doesn't have the privileges of a state either, such as being represented in the US government. This is not easy to fix; giving DC state privileges would be a severe blow to the idea that the federal government doesn't favor any one state over another.
It still gets taxed, though. People are sore enough about this that when someone submitted the suggestion of "no taxation without representation" for the slogan on DC license plates, it was vetoed by DC government for being "too controversial".
I would actually be OK with saying that DC doesn't get taxed, since they're legally prohibited from participating in the government. But I don't think that's a widespread viewpoint. Do you have an opinion?