“Christ would be added to Buddha as a god or guru, and Christianity would at best become another sect of Hinduism.”
Why would that be bad? Why are so many obsessed with the repudiation of the beliefs of others rather than with the wider acceptance of their own belief? Nobody is asking those who believe in Christ as the only savior to change their belief. How would it matter if Buddhists & Hindus accept the teachings of Christ but not necessarily the contention that no other path exists? Would they not be benefitted by the teachings of Christ? Is it anyone’s argument that the teachings have no intrinsic value by themselves and serve no purpose unless it is also accompanied by the total repudiation of other beliefs? Even if that be the argument, why impose it on Buddhists & Hindus who do not share that conviction?
That statement isn't correct anyway. If Hindus made Christ a deity that would be a change to Hinduism not Christianity. Christianity would remain as it was. It might irritate some Christians with OCD but it doesn't do anything to the faith or its followers.
Well, yes. That was the argument of Christ and the early Christians, more or less. They did not (quite) say Christ's teachings had no value unless all other beliefs were rejected. But they certainly said a Christian could not continue to believe anything contrary to what Christ said and remain a Christian.
Christ himself said salvation could come only through Him. That means unless you accept Christ as the Savior, honoring his teachings as moral precepts have no value for you as an individual in the long run. In fact, if you reject him as the sole Savior, you are by definition not honoring his teachings, since you are deciding on your own authority which of his sayings are valid.
Even if that be the argument, why impose it on Buddhists & Hindus who do not share that conviction?
Where, in the last century or two, have Christians "imposed" their arguments on Buddhists and Hindus? If I believe strongly and make an argument for my opinion, is that "imposing" my views on the hearer?
Another reason why: Christ told us to. He ordered his followers to preach his Word, including most especially the part about him being the Son of God and the Savior of the world. He did not order them to go forth and devote their lives and suffer horrible deaths to promote the idea he was just another in a long line of good moral teachers. That would have been a remarkably silly thing to do, and even Monty Python couldn't really find much silly in Christ's teachings.
How would it matter if Buddhists & Hindus accept the teachings of Christ but not necessarily the contention that no other path exists?
Because the core teaching of Christianity is that no other path to God and salvation exists?
Because if that teaching is abandoned Christianity in any meaningful sense ceases to exist?