The government needs to get its money from somewhere. If it spends the taxpayers' money, that money cannot be spent on other things. So instead of doing things that are useful to society, like maintaining roads, the money is just sitting there until the bond matures. If it creates money out of thin air, the effect is the same, except that now every market participant pays (in the form of increased inflation). So in either case, the losses are socialised.

Of course, you can still argue that stabilising the system is worth it.