Why do you think the US has global power projection capabilities? Why do you think they can control world trade? Why is the dollar still the reserve currency?
The military "altruistic" peacekeeping is a major benefit, from better access to trade agreements to bases everywhere and military support from dozens of countries.
Nothing of that would be possible otherwise. Ending the US' protection also means taking away a massive piece of global influence the US had and turning into a "normal" country, not one the world seems to revolve around.
That's the trade-off. You can't keep the soft power without having partners who rely on you and are going to have a much, much harder stand in future negotiations.
Also, US military spending goes directly back into the US economy. This is absolutely not the same as paying other countries, it's a hidden, long-running stimulus for the MIC.