Why does everyone hate vent?

So i see this again and again all the time i lead a raid. It usually goes like this. I post vent info for a current tier raid or sometimes 5.1 raids. And first thing i see "Seriously we need vent for this? wtf" "I'm not getting in vent I know the fights", Is it really that hard to get in vent to hear the call outs? Like I have a hard time seeing how these people that are so anti vent can even raid at all. It doesn't make any sense to me. Why is so hard to just get in vent? Are you going to die if you have to hear the call outs? Are you seriously thinking that everyone running a particular raid is using the exact same strats on every boss? Seriously people there are multiple strategies for every fight not just the one you were taught when you killed it and call outs being made asking for raid cds or healing CDs etc. And i can tell you from a dps standpoint particularly on my dk If you have no clue when the raid lead is calling for lust You can really suffer a dps loss.(I.E. I play Unholy so If i line up my cds and as soon as i pop my unholy Frenzy the raid leader calls for lust I would feel really retarded and then get laughed at for wasting a cd). So what gives why does everyone hate vent so fiercly they would rather leave a group then get in vent to do the raid they asked you to join?