ANSWER: When Jesus observed the needy widow contributing two coins of very little value it was immediately after he had thrown the money changers out of the temple and right before he announced that the temple was going to be thrown down without so much as a stone being left upon another stone. The point is: Although Jesus knew that many of the priests were corrupt and the temple was going to be demolished he still commended a worshipper who dropped a very small donation into the temple treasury.
By the same reasoning, even though there is a corrupt element within the leadership of the Watchtower Society and the funds of generous donors are misused on secretive out-of-court settlements and lawyers fees to prevent justice being carried out, still, the organization is accomplishing a great work in producing Bibles in hundreds of languages and useful literature that has aided millions to come to a basic knowledge of the Bible.
Obviously, individuals who donate to the Society cannot dictate how they wish their gift to be used; but ultimately, it is they who will have to answer to the Master for how they have used the funds entrusted to them. In that respect, then, those who contribute to the Watchtower can do so in good conscience.
As regards charitable organizations they have their problems too. Many of them have highly paid executives and spend huge amounts of money on nothing more then raising more money. It is not uncommon for only a tiny percentage of contributions, if any, to be used for the intended cause.
On the other hand, there is another aspect of giving that you may want to consider, and that is giving directly to individuals in need. Jesus once remarked that we will always have poor people among us and we can give to them whenever we wish. And unfortunately due to the disintegration of the economy their numbers are growing and will continue to do so. There may well be individuals or families in your congregation that are in need. And keep in mind that the scripture says, that those who help the needy are loaning to God himself. What a privilege!
As far as using contributions as a tax deduction, you make a good point. Jehovah loves a cheerful giver, but if our giving is motivated by such self-interests, is it really giving?
Sadly, the WatchTower actually appeals to Jehovah’s Witnesses every year toward the end of the tax year to make big tax-deductible gifts.