Christians don't represent 70% of the population. They represent 70% of the people who declare themselves "believers", which is not the same at all. ^^
About half of the French consider themselves atheists, so the 70% number is technically impossible. Religion is "tolerated", not part of our daily life, not linked to the politics and we have "laïcité", in other words one should neither impose their beliefs by strongly showing them or make others follow them too.