Assuming you're purchasing from someone with infinite carbon credits and you're spending it in an environment with infinite ability to re-sink the carbon. Sure.
To a more and lesser degree depending on the action, I try to apply "that rigor" to myself, at least?
And yes, I think the world would be better off if more people considered how their decisions impact others, if that's what you're getting at, but it's unrealistic to expect everyone to care about other people - and of course entirely impossible to account for ALL variables.
How do you come up with a ratio that you consider a fair trade?
I'm really not sure how I'd personally set a metric to decide it. I could go with the stat that one barrel of oil is equivalent to 25,000 hours of human labor. That means each barrel is worth 12.5 years of labor at 40 hours per week. That seems outrageous though - off hand I don't know how many barrels would be used during the flight but it would have to be replacing way more than several engineers working for several years.
Seems like a fair carbon trade.