I agree with Dreams. For half a century we have been very lucky to enjoy an unprecedented level of security and safety. And in England we rarely face earthquakes, typhoons, bush fires, and other natural disasters that other countries cope with.
It depends on your balance between risk and a view that unless you don't take a "life must go on" approach your, or your DCs, lives will be poorer. I live in Central London and there is always a nagging concern. The risk is probably as great as that in Paris. But then I lived in London through the IRA attacks, so it has always been there. Equally I know people who choose not to visit London because of that risk.
Schools/tour operators have a duty of care and so will weigh up risks. However, as with other things like sport, they have to also work out a balance between that and giving their pupils educational experiences, encouraging a wider world view and increasing their aspirations. If you find yourself more risk adverse than the school, ask for your child to be left out, but do not ask for the trip to be cancelled. That would be unfair on the others.