buy and read born to run and then hand it over to your friends. :)
there are many threads about this issue on backpackinglight.
one needs trained feet to be able to hike safely in trailrunners. and one has to try it out, before judging the whole thing. most doubters do not have any first hand experience to back up their claims at all.
go try it out for yourself, it doesn't matter what your friends think. in terms of training: it usually works for me to just walk barefoot at home and in the garden, and partially walk to work. no special training is requiered for me.
Roger's faq is still up to date and goes into detail:
boots make sense if it comes to mountaineerinng, ice climbing, skiing and in the deep winter.
I rather think that most of the foot impact is caused by the load one carries.
And nothing is 100% safe, if someone falls or slips badly even boots won't help. The whole ankle support thing is just a marketing myth most of the time.
I have seen people hurting them self wearing big boots and carrying heavy packs. I would rather say that some injuries are rather caused by heavy boots.
Just show you friends how many people do thru hikes with trailrunners if they are still not convienced. Someone hiking 2000 or miles usually knows and has tested what works and what not.