This is simply not feasible without a conscription.
No, I did not like my conscription (Finland) two decades ago - but I completely understand why it's necessary.
What you get, though, is effectively a sleeping guerrilla organization that can be mobilised to resist occupation. Very basic military skills can be very effective in such a scenario, which is the most likely one for countries bordering states with overwhelmingly larger arsenals.
This highly dependent.
For example, Finnish Defence Forces are capable of very professional response to external threats.
Remember this leverages the entire eligible male population that is highly educated, motivated, and culturally aligned to follow chain of command.
There is also the backbone of professional, university trained officer core who manage all of it.
Some of the most technical service branches like the air forces utilize professionals extensively as well.
I've always liked the idea of mandatory civil service; one option being the military. Having family in the military and being exposed elsewhere, it's interesting to get a closer view of the parts of government we pay for, like missile silos or aircraft carriers, but often put into a black box. I would hope it would make people more civically aware and engaged. I've been curious about contributing to something like 18F or US Digital Service. Do any countries do this?
From a pure defense perspective, nothing beats a conscription system in efficiency. Here in Finland (population about 5,5 million) we have a reserve army of 900,000 people. With a pure salary army, it could be maybe 2-5% of that.
Cons: takes 6-12 months away from your life. But my and virtually anyone I know has the opinion is that it is also a very valuable life experience and I carry many lifelong friends from that time period.
Here, conscription was even considered a way to balance sex-related work opportunities, since it was a burden on men only, hence women who entered the workforce were a bit advantaged.
I agree that the experience can be good, but YMMV a lot: many of my friends were happy to serve and learned a lot, but many others were shocked and some never fully recovered. Such a life won't fit everybody.
Also, it takes quite a lot of time in your life even when you would like to do something else. I think that a "serve your country" 6/12 months period, to be done by everybody by the time you're 25 or so, that you can plan, could be useful.
This is because serving in the military is a civic duty, not just a sort of commercial service. The military is not just supposed to be a hired group of fighters.
https://en.wikipedia.org/wiki/Sortition#Ancient_Athens
EDIT: I remember this from a Historia Civilis video:
You should watch the whole thing (it's pretty interesting) but skip to 8m00s to watch the part about sortition.
Which I find surprising, because my (admittedly somewhat limited) understanding is that the fear of established, professionalised, closed-up armies is actually a very ur-American idea, threatening peace, equality and so on. I guess the same could be applied to a lot of the over-militarised police and border agency situations that hit the news all the time. Civic oversight and less professionalisation, more popular control I always thought would be natural ideas across the pond.
Indeed; if you read the documents, antipathy to the concept of a standing army is a primary motivation for the second amendment.
Secondly money and conditions can't be universal drivers.
On a side note I feel trend of letting youngster do whatever they want even during school years is counter productive. For example children who misbehave even once in a while with teachers and sometimes parents even are taken for psyche evaluation immediately. IMHO children does need direction and guidance until they understand the consequences of their choices.
Those that would volunteer are not necessarily the ones you would want.
There are always going to be a social contract, things you have to do, like paying taxes. I would argue that defending the country is a reasonable thing to include in that social contract.