People in Britain are in danger of becoming "too hysterical" as a "national culture of fear" develops about the threat posed by radicalised Muslims, the archbishop of Canterbury, Justin Welby, has warned.

Some radicalised young people are travelling to Syria but Welby said the number was "extraordinarily small".

He said differences between Christianity and Islam were no excuse for hostility.

In a wide-ranging interview on the Andrew Marr Show on BBC1, Welby also said:

• People would find it incomprehensible if the Church of England refused once again at its Synod in York this week to vote in favour of ordaining female bishops.

• The Church of England faces an unstable future over gay marriage. Welby said he was opposed to gay marriage but confirmed that he had been struggling with the issue.

• More cases of child abuse in the Church of England were likely to be uncovered by the new public inquiry led by Lady Butler-Sloss.

• Rich people have a duty to pay their fair share of tax. He condemned aggressive tax avoidance.

On the threat of radicalised Muslims, Welby said it was important to keep matters in proportion. He said: "Clearly there is an issue with people going to Syria and coming back highly radicalised. There is a problem with radicalisation. But the proportion of Muslims who are radicalised is extraordinarily small. I am just edgy about developing a national culture of fear because I don't think that gets us anywhere.

"I think we are in danger of slipping into a very fearful culture in which we see everyone against us and us against everyone and we are constantly trying to defend ourselves. This country is much bigger than that, much better than that."

Asked whether Britain was becoming too hysterical about the matter, Welby said: "We have been becoming too hysterical about this subject for some considerable period. It is a worry because we have huge differences with Islam – as Christians. But that is absolutely no reason for hostility. Quite the reverse."

Welby was speaking to the BBC as the Synod of the Church of England prepares to vote again on whether to ordain women as bishops. The archbishop suggested he was confident of victory but warned that a loss would dismay the public.

Welby said: "To the general public this is almost incomprehensible. It is equally incomprehensible that we are still talking about it."

The archbishop said he was still opposed to gay marriage but made clear that he had been giving the matter deep thought. He said his heart went out to same-sex couples, including Anglican priests, who would like to marry.

"I have not been convinced by the arguments for same-sex marriage as marriage. I continue to struggle with the issue. Pastorally you meet people, sit across the room from them, some wonderful priests. Your heart goes out to them," he said.

"We are in the middle of a prolonged period of disagreement and conversation and therefore by definition it is unstable. That is something we have to deal with."

The archbishop, who first made his money as an oil executive, quoted the Bible as he spoke of the need to pay tax and not resort to aggressive tax avoidance. "Funnily enough there is the passage in the Epistles to the Romans that says: pay your tax. People have a duty to make a proper contribution to society proportionate to their income. If they are doing very well they should be paying quite a lot. There have to be serious questions about some of these tax avoidance schemes.

"There are very few of us who find it easy not to have sticky fingers. We all quite like a bit of money – usually a bit more than we have got. There is an obligation to the common good."

Welby warned that more cases of child abuse would be uncovered in the Church of England. Asked whether more cases would emerge, he said: "I would love to say there weren't but I expect there are. There are in almost every institution in this land.

"It is becoming clearer and clearer that for many, many years things were not dealt with as they should have been dealt with. We must show justice to survivors of abuse."