Thomas

Jesus saith unto him, Thomas, because thou hast seen me, thou hast believed: blessed are they that have not seen, and yet have believed.

is a direct allusion to those who like to say

Seeing is believing.

so why would the Portuguese have called the Hindus Thomas Christians?

It's the kind of question that modern historical science cannot give the answer to, because Vasco da Gama didn't actually write it down. Yet to any thinking man it's clear that Hinduism's focus on performing miracles is the reason.

Considering this Christ speaks the historic truth, for Europe has been blessed more than India. But why is blind faith better?

Like everything, I think it boils down to efficiency: For one it's easier to study at a university than to acquire the favour to perform miracles and for another it's easier to form a hierarchical organisation based on voting than on recognition of grace.

But there is one catch of course, namely that you have to believe. If you do not believe without seeing, then it is better to see.

I know from personal experience that monism sharpens one's sense of one's transcendent connection and that that in turn raises one's expectation of the effectiveness of prayer, which in turn makes it more likely that a prayer will be heard, and from there on out the seeing part begins.

It is said that Christ will not find belief on his return. It is also said that in those days even the maids will prophesise. Seeing is believing might be the link there.