I'd imagine there are many pacifists who would really rather not pay for defense through their taxes.
As you say there are different ways of paying for things and often the key question is which method is best. Of course even then the question "best for who?" comes into play.
Any system that gives out free money will be abused. It's human nature - why work if you can simply game the system and get as much money for free as you might have earned by working? Especially for the people at the bottom of the economic spectrum who may not have much in the way of employment prospects beyond minimum wage jobs where they may get minimal notice they are needed at work, and gaming the system not only means they get comparable money without working but they also get to plan their weeks because they know they won't suddenly get a text message saying they are needed at work this evening. As with so much else it becomes a question of balance - too far one way and the system struggles under the weight of people fleecing the system; too far the other way and the people in genuine need are abandoned to the mercy of whatever they can scrape together.
Bundling healthcare with employment does create problems, as you say. Breaking healthcare away from employment would certainly have benefits but would also have costs. Just like the "Affordable" Care Act had many winners but also had many losers, and objective discussion proves increasingly difficult as many people simply fall back on their preferred mantra of "my premiums have tripled" or "are you trying to take away my insurance?"
Even single payer is fraught with problems. In the UK the NHS is free at the point of use (note that it isn't "free" because someone has to pay) and is riddled with all sorts of its own problems. Firstly there's a huge amount of waste, waiting lists can be staggering, people frequently find themselves caught up in a "postcode lottery" where they find that their own local health authority won't fund a treatment but if they lived half a mile away they would be under a different authority that would find it. And then comes the problem of just getting to see the doctor in the first place. In the US it's easy to see the problems that something like COVID-19 presents, if people don't see the doctor because they are afraid of the potential bills (and a $5,000 deductible is a pretty powerful disincentive to see the doctor). In the UK when the doctor's office gets swamped you might have to wait 2-3 weeks to see the doctor, which would have much the same overall effect. For example, I had a friend who was having chest pains in his 20s and the doctor couldn't see him for three weeks, so he ended up going to the emergency room (thankfully his heart wasn't packing up). The NHS also has problems with people who just don't show up for appointments and don't bother cancelling them, but also has problems when people do cancel their appointments and the system doesn't register it, prompting them getting a nasty letter about wasting resources. The NHS also does all sorts of unhelpful things to try and scrub up a bit of cash, from charging for parking (it's always fun when you paid to park only to find your appointment is delayed, and you don't know if it's safe to go and pay for more parking because if you're called while you're feeding change to the meter you'll get tagged as a no-show, but if you don't go out then you'll get a heavy fine for overstaying your parking ticket), to charging for TVs at the bedside (good luck sleeping on the ward if someone else on the ward is hard of hearing and has their TV on loud at 3am - apparently their right to watch TV trumps your right to sleep).
A major problem with the concept of "health insurance" in the US is that much of it isn't actually insurance at all. Insurance is about the transfer of risk, so coverage for pre-existing conditions can't be considered "insurance" - to ask an insurance company to cover a condition that already exists is akin to trying to take out fire insurance after your house has burned down. Of course people with conditions need to be treated, and the notion of insurance running in discrete 12-month windows just complicates the best way to go about providing treatment. Likewise expecting routine maintenance to be covered by insurance would be akin to expecting your car insurance company to pay for new tires and oil changes.
And hence the question comes back to the simple one, who should pay for healthcare? It's easy to see why something like treatments for cancer should be funded through taxation because many (most?) people who are diagnosed with cancer haven't necessarily done anything specific to cause it. But what about things related to obesity or smoking, just to give a couple of examples? Should a heavy smoker who is diagnosed with lung cancer or emphysema be treated on the public dime? Should the 450lb person who is diagnosed with diabetes be treated at no cost to themselves? Even without looking at people who are obviously unhealthy, should a super-fit mountain biker who crashes their bike and needs major reconstructive surgery have to pay towards the cost of their treatment? And in a system where there is no cost at the point of use, what steps should be taken to prevent the abuse that will inevitably occur? An example here - a doctor friend of mine recently posted an article about an elderly person who died, leaving many thousands of pounds worth of unused medication. They had collected all their prescriptions (not paying anything for them, due to their age), they just didn't actually take any of the medicines. So the NHS paid thousands for the drugs that ended up in the trash. Even a modest charge encourages people to consider whether they really need the medicine, but even a modest charge can prove prohibitive for people at the bottom end of the income scale.
