Can we please differentiate here. Let's look at it as two sides of a coin. On one side we have the obeyance of the rule no matter what. You will find I have agreed with that already earlier in the thread.
No, you can't have it both ways, because you're directly contradicting yourself. You can't say it's their right to decide what you're allowed to do to THEIR body, then say 'unless it's for a bad reason'. It's just not up to you. Sorry. Your opinion, no matter how correct and brilliant and insightful, just doesn't MATTER.
It's not like it's even that hard to convince someone to go really slowly and show them you'll keep going really slowly and let them discover for themselves that it doesn't hurt as soon as they thought it would. I've done that more than once, and I'm not even particularly advanced, nor do I claim to have your exceptional judgment or ability to read the situation. If you go slowly and smoothly, you don't even HAVE to be a genius or know your partner better than they know themselves.