It's a tough argument. The perception towards spreading Christianity wouldn't change by stopping the aid, it will change by stopping the spread.

Now, do I advocate banning such "preaching" in Nepal? I absolutely don't. Every religion should have the right to spread its message freely, without imposing itself or forcing anybody. On the same token the said religion should also know that it will meet the impediments from other existing religion. Having said that, no religion should have the right to force their preaching to a group, or stop any other religion from preaching, by means of violence.