There's a difference that Ukraine had not much choice after being invaded but a larger enemy, aside from maybe surrendering and letting Putin take over. Russia's invasion however was almost entirely their choice and could be stopped tomorrow if Putin just told them to stop.
That's a bit of a false dichotomy as the early terms were relatively modest but, in general terms, I would agree with the point you're making. However the issue you run into is that the exact same arguments were made in favor of slavery. For instance even Aristotle some 2400 years ago predicted the end of slavery, if slaves only were not necessary:
"For if every instrument could accomplish its own work, obeying or anticipating the will of others, like the statues of Daedalus, or the tripods of Hephaestus, which, says the poet, 'Of their own accord entered the assembly of the Gods.' If, in like manner, the shuttle would weave and the plectrum touch the lyre without a hand to guide them, chief workmen would not want servants, nor masters slaves." [1]
Of course society could have gotten by without slavery, but it wouldn't have been as convenient, particularly for the wealthy and political classes who were the exact sort that could afford to own slaves. And the exact same is true of conscription. If people are not willing to die for the political class of a country, who are the political class to insist they die for them? And the greatest irony is that the most 'brave' of the political class are often made up of cowards and draft dodgers themselves. But it's an entirely different game when it's not their life on the line anymore.
People, who live in a time when humans in warfare are obsoleted, will look back upon this as even more vile and barbaric than slavery. And they'll damn us all for it. Yet it's an issue that "we", the people without power, mostly do not even really think about one way or the other - because it's just how it is. We might speak out against it, those in affected regions might even start their own 'Underground Railroads' to escape tyranny, but everybody knows it won't end.
