...what?! You can't be serious. Do you take your used condoms with you too?
With perfect use, condoms have a failure rate of 2%.
This is a CHILD we're talking about, not something transitory. Do you gentlemen really worry that an escort will want to have your child and then ask for child support? What about the ramifications of that act for her? She has a child with someone she doesn't know and can't explain, that's going to impact her life significantly! Because, y'know, she'll
have a kid and stuff. Not to mention that in this absurd world where an escort a) gets pregnant b) decides to give birth c) decides to notify the client, how is she going to know which client it was, even if she's only moderately actively working? I'm going to say it'd be difficult to predict the race of the baby, nevermind the father...
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Why don't I swallow? It makes my stomach hurt sometimes. I don't like when my stomach hurts and I can't predict when it will hurt or not, so I don't do things that might lead it it happening, just like if you have the option you'd probably also avoid things that make you uncomfortable and almost certainly in an escorting setting. Maybe it's psychological (like GPIDEAL said) but that doesn't change the end result of 0.1-1.0 mL of egg-white-consistency cum in my stomach.
(There's also an argument to be made for keeping services standard across the industry; once it becomes 'the norm' those who are uncomfortable with it feel pressure to do it. Note the progression of BBBJ from 2007 until now...)