Cannot agree that it has anything to do with so called 'class'.
I was brought up in a working class home if you base that assessment on my father's occupation, and have NEVER used the glottal stop. And never will.
It's just lazy speech or people trying to fit in by speaking the same as the majority of their friendship circle, or both.
Or, sadly, it can be to do with lazy parenting or teaching.
Personally, I just couldn't bear to hear myself saying le**er or similar.
I also have a hang up about written words. I write a column for my local paper every couple of months and when proof reading, find myself having to change "I have" into "I've" , or "cannot! into " can't" etc, as the way I was taught to write in school is still engraved on my brain, but sometimes I realise that my rants ( more often than not) just sound too stilted otherwise. At least it's still correct English!