Non citizen permanent residents are just as affected by elections and the government as anyone else. The citizenship process is long, expensive and difficult. Those who reside in the US all deserve the right to vote just as citizens do. Anyone who is impacted by government has the right to influence it.
It's actually pretty easy to become a citizen, so I don't see why the resident aliens wouldn't just BECOME A CITIZEN if they wanted to vote. This isn't a complex thought process, really, it's just narrowing down why you should be a citizen. Resident aliens already have many of the rights of citizens, but some things should be left to the citizens.
Those who support this thoroughly backward idea argue that it would encourage newcomers to take part in the civic life of their new home, fostering a sense of belonging. It is more likely do just the opposite. The best path to full belonging is to become a citizen, and letting non-citizens vote removes an important incentive to take out citizenship. In the words of Councillor Denzil Minnan-Wong, it “devalues, degrades and erodes what citizenship means.”