This argument that everyone's vote or at least the default method of voting MUST be absolutely inviolately private and secure while our most personal conversations and details of our lives be matters of government scrutiny seems, to put it in the most charitable light, "inconsistent".
A much more plausible explanation would seem to me to be that making voting more accessible regardless of security implications will change the voting demographics in ways that haven't been vetted and agreed upon by both parties in our two party system.
That hasn't stopped claims of up to three million illegal immigrants voting in the presidential election [1].
We know of course there's some illegal immigrant voting (no voter ID laws in some states + lots of illegal immigrants in those states + some very big motivation to vote = yes, of course they'll vote). We just don't know how much. Is it closer to 3 million illegal immigrant votes, or closer to only 30,000 votes?
Trump warning about rigging won't prevent illegal immigrants from going to the polls organically. However, it does put a damper on any potential plans the DNC might've had to have voters drive to critical districts and place votes there, as they've supposedly done in the past [2].
That said, I have a hard time believing the DNC could mobilize enough voters to really change the polls, even targeting key swing counties in key battleground states. Far more likely are rigged machines, like those encountered in early reports in Texas [3].
Of course, anything is possible - Trump could've done some rigging himself! But normally it would be counterproductive to seed the idea in everyone's minds that an election is rigged if you intend to rig it. Just because you won doesn't mean the meme goes away. You just create problems for yourself after you steal the election. Far better to play it like Hillary Clinton and calmly dismiss any talk of rigging: "Oh, posh, there won't be any rigging. Don't be silly!"
Also, as Clinton so aptly pointed out in the third debate, Trump has a tendency to accuse anything he might not win of being rigged (like the Emmys). This is more a general strategy of his than anything else. It's analogous to how ball players and coaches yell at referees that their play calling is atrocious and one-sided, in the hope of influencing things to go their way. In this case, Trump was likely whipping up his base + aiming to discourage any possible / prospective plans to rig things on the other side.
[1] http://www.thenewamerican.com/usnews/immigration/item/24630-...
[2] https://www.youtube.com/watch?v=hDc8PVCvfKs
[3] http://www.zerohedge.com/news/2016-10-25/texas-rigged-first-...
Can you provide some corroborating evidence for that?
In response, the opposition made strong claims that elections cannot be rigged, in spite of the verified evidence of experts that they can be rigged.
Net result: Trump wins an 'upset' election, that was actually rigged in his favor, whilst the opposition cannot bring itself to claim that is was rigged, as that would be a contradiction of their earlier defense of the voting system's integrity.
There already exists a flawless system for ensuring 100% accurate voting results: a distributed consensus network utilizing a public block chain. Voters get assigned public/private key pairs upon registration. Their vote is a simple transaction on the blockchain which they can validate anytime they want.