Outside the human body, MRSA is just as susceptible to disinfectants as any other bacteria. Like E. coli, it's when it gets places it doesn't belong that it's a problem.
Well, not any
other bacteria. Bacterial vulnerability to disinfectants is going to vary wildly depending on the constitution of their capsule, cell wall, cell membrane and other structural factors. This is what allows them to live in a multitude of absurdly hostile environments. But that is nit-picking, as yes MRSA is just as susceptible as any other bacteria that tends to thrive within the same environmental parameters as we do and infect us. Alcohol sterilization has been shown to be effective on MRSA and is a great line of defence.
And you are exactly right. The harm that bacteria do depends on them getting to where they don't belong. Most everyone has staphylococcus aureus
on their skin. And you most likely touch hundreds of things every day carrying a load of bacteria that if it became entrenched in the wrong place at the wrong time could cause serious medical problems. Bacteria are like cattle. It isn't so much that they are out to get you, but more that if they get into the wrong place they will A)consume useful nutrients, and/or B)excrete a ton of waste.