You are exploiting a philosophical conundrum (the sorites paradox) and apply a logical fallacy. As a general result, if you follow it your flawed logic, no one would ever be able to make any decision at all.
Yes, you are being absurd, but not at demonstrating absurdness... What you call absurd, is reality, the reality of setting boundaries, which are not at all absurd. Heck, with your 'logic', linguistic concepts could not even exist.
Why tax at 15%? If you can get away with 15%, you can also get away with 14.999999999%, if you can do that, you can also tax at 14.99999998%, and reason all the way down to 0%. Or it wouldn't matter if we taxed at 100% either, because 15% is basically 15.0000001% and up we go.
Here is another one for you. How many sand kernels make a mound/hill. Surely not 1. 2, don't think so. 3, nope. 4? Not yet, and we keep on going. What if we hit 15000, or perhaps 15001, what about 15002. But if 15002 sand kernels make a mound, why, then clearly 15001 and 15000 also make a mound, and back we go...
If you can take an image every nano-seccond of a developing frog egg, all the way to a tadpole and then eventually into a frog, can you point at the definitive image that shows you were the tadpole turns into a frog? You can't and yet we have a frog and a tadpole. (Also try it for the development of a human being, from an inseminated egg to an embryo)
What a about a plant, let's say a tree. When does a seed become a tree? Now, it's a seed, but at one point we call it a tree. Is it now a tree? Or now? Or now? What about in a minute, and hour, days, months, years?
Here, read it also on wikipedia, how absurd your proposition is:
The continuum fallacy (also called the fallacy of the beard[1], line drawing fallacy, bald man fallacy, fallacy of the heap, and the sorites fallacy) is an informal logical fallacy closely related to the sorites paradox, or paradox of the heap. The fallacy causes one to erroneously reject a vague claim simply because it is not as precise as one would like it to be. Vagueness alone does not necessarily imply invalidity.
The fallacy appears to demonstrate that two states or conditions cannot be considered distinct (or do not exist at all) because between them there exists a continuum of states. According to the fallacy, differences in quality cannot result from differences in quantity.
There are clearly reasonable and clearly unreasonable cases in which objects either belong or do not belong to a particular group of objects based on their properties. We are able to take them case by case and designate them as such even in the case of properties which may be vaguely defined. The existence of hard or controversial cases does not preclude our ability to designate members of particular kinds of groups.
Examples
Fred can never be called bald. Fred isn't bald now, however if he loses one hair, that won't make him go from not bald to bald either. If he loses one more hair after that, then this one loss, also does not make him go from not bald to bald. Therefore, no matter how much hair he loses, he can never be called bald.
http://en.wikipedia.org/wiki/Continuum_fallacy
The word "sorites" derives from the Greek word for heap. The paradox is so named because of its original characterization, attributed to Eubulides of Miletus.[1] The paradox goes as follows: consider a heap of sand from which grains are individually removed. One might construct the argument, using premises, as follows:
1,000,000 grains of sand is a heap of sand (Premise 1)
A heap of sand minus one grain is still a heap. (Premise 2)
http://en.wikipedia.org/wiki/Sorites_paradox
Just "play along with the 'group think'".... It's called reality.