Except we're talking about income tax. In my scenario Bob pays 25%. I should know, it's my scenario....
And how do you know how much they are going to have to increase taxes? They aren't just adding basic income and leaving everything else the same. Every single other welfare program would be scraped and the money rebudgeted towards basic income. No more medicare, no more subsidized housing, no more old age pensions, no food stamps, no employment insurance, no more welfare, no more subsidized bus passes, no more anything. My 10% increase is literally just as valid as your 40% because neither of us know exactly how much it will need to be adjusted after all budgets have been reworked. Hell they may not even need to increase taxes at all once they get rid of all the administrative overheard of separate departments.
Again, you keep bringing up the slippery slope. They aren't going to tax people to the point where they make LESS than they would on basic income. If you are working you will always be able to buy more than those on basic income.