1. Could you elaborate on this? I have to claim naivete on that one. I generally don't buy a lot of stuff online but it's a non-zero thing.
2. I've done some domestic and international travel and have never had a problem. In my case, all I had to do was preparation and due diligence beforehand.
I'm not Sibley but I'll try to answer your questions.
1. Using your credit card online is generally riskier than using it at a brick-and-mortar store. There are more opportunities along the way for someone to steal your number and use it for unauthorized purchases.
With a CC, if only your number was stolen but not your physical card, you're not liable for any of the charges. With a debit card, you can be liable for up to $50 if you report it in 2 days or $500 if you report it in 60 days.
CCs often also have additional protections around purchases that I've never seen from a debit card. Stuff like, "That thing you ordered from a random website wasn't as advertised and you've tried to go through their return process with no luck? No worries, we'll just refund your money and deal with the merchant for you."
2. If you haven't had issues, great, but I always see stuff about $500 hotel or rental car holds on debit cards, which never happens for CCs. Also most travel-reward CCs include some amount of travel insurance or rental auto insurance in their benefits.
All in all, credit cards are a tool. They can be dangerous in the wrong hands, they can be misused. In my nearly 20 years of using them, I've paid exactly $0 in interest, and have slowly progressed to more and more advanced uses of CCs (multiple rewards, churning, tradelines).
Making "I've never had a CC" A Thing for you might make sense if you think you might be prone to misusing one. But your description of others' CC debt doesn't sound like that. So it kinda becomes like making "I've never used a power saw" A Thing. Sure, you can do great things with hand saws, and they're safer than power tools, but why not use the best tool for the job?