I sort of know I'm not being unreasonable so this is probably more of a rant than anything!
A while ago I went to my friends mothers house with my nearly 4 yr old, she had a trampoline in the garden which my little on went on, my friend then took her baby inside and saw her mum, I stayed in the garden, it was quite big, fenced but with a small gate at the bottom that we came in from, bust residential area and a lot of roads around
Anyway my friend came out and said 'leave DS there he will be fine come have a cup of tea'
The way the house was facing there wasn't even a window I could view DS from if I went inside
Anyhu I said no I couldn't leave him on his own out there and then we had a long discussion about how I was smothering him if I didn't let him do things! 
I listed off the top of my head things that could happen if I left him, he'd never been there before so it was unfamiliar, he could fall on the trampoline, he could go out the gate and get lost/run over/picked up by someone! Only to get accused of being anxious!
I was happy outside, my DS was happy, I wasn't stood there on my own rocking and listing all the things that could go wrong, I was just pointing out, as I think most parents do, you're constantly risk assessing things unconsciously, it doesn't make me anxious it makes me a mother!
We didn't fall out or anything but it just really annoys me that she thinks leaving him totally on his own would be OK, aside from the fact that I actually want to spend time with my DS she couldn't acknowledge it probably wasn't totally safe! 