I see what you are saying, but it's not pointless, you are just missing the points. The first point is a matter of perceived fairness, and thus political viability. If people think that a proposed system is more fair than the current system, then they will be more likely to accept it. The second point is to eliminate the possibility that taking away or reducing the government benefit will be a disincentive to earning a larger income. If someone making $100k has to pay an extra $10k to get that $10k back as a BIG, then it's a wash to them, but this isn't about someone who is in that "wash bracket", it's about people who need that money to put food on the table, or to be able to save for a down payment on a home.
Surrealistik, you see what Thrilla is saying? THAT'S why we shouldn't means test a BIG. Means testing it partially defeats it's purpose, and totally defeats it's political viability. He said he wouldn't support a means tested BIG, and neither would I.
I bet you could tally up the positions of the dozen or so posters on this thread, and you wouldn't come up with enough supporters of a means tested BIG for support to reach the 50%+1 level. You remove that means testing, and I assume that you have gained Thrilla, and I know you have gained my vote, so that's an increase of about 20-30% support, which very well may be enough to make it politically viable.