Just read them this scripture.
" Having heard everything, I have reached this conclusion: Fear God and keep his commandments, because this is the whole duty of man." Eccl 12:13 :
I don't see "activity X" in there do you?
If they keep on about it, flip over to Eccl Chapter 3:
(It reads better when you sing it in tune with the 60's song that borrows it)
A Time for Everything
1 There is a time for everything,
and a season for every activity under heaven:
2 a time to be born and a time to die,
a time to plant and a time to uproot,
3 a time to kill and a time to heal,
a time to tear down and a time to build,
4 a time to weep and a time to laugh,
a time to mourn and a time to dance,
5 a time to scatter stones and a time to gather them,
a time to embrace and a time to refrain,
-Also-
12 I know that there is nothing better for men than to be happy and do good while they live.
And so on. Just keep singing and reading until they say "OK, OK I GET IT DAMMIT!!"