I think the fundamental moral dilemma for moderates is that both far wings of each parties are taking the respective parties hostage, leaving many people feeling unrepresented and casting a "fuck it" vote.
Trump obviously conducted a hostile takeover of the Republican Party (PBS's Frontline episode of "Trump's Road to the White House" is terrific). He is doing conservative things like lowering taxes, nominating conservative judges, promoting de-regulation, etc.; but he is also a buffoon, as already documented in this thread, and he is not at all old school conservative (small government, budget reduction, etc.).
In my view, progressives are similarly undertaking a hostile takeover of the Democratic Party. Their positions are so incredibly antithetical to many moderates' positions. In no particular order:
(1) they support state-sponsored healthcare for undocumented immigrants (which every D candidate said they would do in the last debate, in an obvious attempt to pander to the progressive base);
(2) advocate for de facto open borders (as described by Mother Jones of all outlets --
https://www.motherjones.com/kevin-drum/2019/07/are-democrats-now-the-party-of-open-borders/ );
(3) unfairly describe wealthy entrepreneurs (according to Progressives, entrepreneurs "did not build" their businesses, which I take great offense to);
(4) want to raise taxes (when I already pay property tax, sales tax, gas tax, liquor tax, state income tax, municipal income tax, federal income tax, medicare tax, social security tax, and healthcare is basically a tax at this point);
(5) expand state-sponsored healthcare and, for some, remove private sector healthcare;
(6) forgive student loan debt (I had $159,000 in loans at the start of the year, and I disagree with this, as it does not solve the fundamental problem -- cost; although I guess this is a popular position because who doesn't want "free!");
(7) The constant, never-ending bashing of American history and achievement (just browsed the NYT to find today's latest: targeting the Apollo accomplishments as sexist --
https://www.nytimes.com/2019/07/17/science/women-astronauts-nasa.html?smtyp=cur&smid=tw-nytimes )
I could go on. So one party is held hostage by Trump, the other by a progressive base that is antithetical to many moderate positions.
There are huge swaths of the middle of the country that do not support Trump or progressives. But when they are picking between the two, they will vote for the one who they think will do less harm to themselves individually.
On this note, I also think a huge problem, for democrats, is that they are kind of the boy who cried wolf. GWB was the devil, now he's revered by many. McCain was the devil, now he's widely revered. Romney was the devil and laughed off the stage for calling Russia our biggest threat, now he's a knowledgeable, noble statesman. I can see why many people just don't give a shit what labels the left throws at Trump.
Bottom line of this rant -- voting for one or the other is a "tacit approval" of everything they do is perhaps true, but it ignores the significant complexities of the matter.