I’m assuming you read this elsewhere because your source does not have a comparrison number. So at present, there is nothing to indicate the number is rising. For all we know the number of people who agree with that type of violence could have been sitting at 16% for many years.
It isn’t realistic to expect the number to be zero. There will always be radicals. Always. Even if we somehow create a perfect utopia, there will always be a handful of malcontents.