A "fervent advocate" refers to someone who strongly supports or promotes a particular cause or viewpoint. They passionately and enthusiastically defend and push for their beliefs or ideas. Full definition
All Else Equal «s central claim is that privately run schools are not always good, a truth with which even the most fervent advocates of school choice would agree. (educationnext.org)
Nonetheless, it underestimates the diversity in culture and values of the American population to take it as a given that we will not see among schools of choice a number that will outrage even the most fervent advocates of the freedom to choose one's school and one's education. (educationnext.org)
It is true that Christianity has had a significant influence on our country but it is not as significant to our modern life and culture as its more fervent advocates claim and that is no reason to think that it should have the lion's share of curriculum time in a subject — like RE — that should be of personal relevance to all young people. (politics.co.uk)