This is indeed a worry & I am not surprised but just to present the facts here not ALL RFDS A/C have TCAS, besides TCAS is fine but only under certain conditions as mentioned amongst these pages. TCAS doesn't separate planes, pilots do:-)
I'd like a dollar for every time I came too close to a pvt A/C especially ones being flown by foreign students under the VFR. R/T is a huge problem out there as well, some really have no basic idea of navigation either preferring to use GPS for ALL tracking situations.
Here's a doozy of an Eg. I was coming into a CTAFR some time ago & was trying to get a picture of where this guy was whom also was inbound to said CTAFR. I asked basic info regarding his position. You know radial or brg from the station distant out etc.This guy stumbled, fumbled & in the end had no idea where he was in relation to any aid. In fact he started to get very nervous on the radio & mucked up all the radio calls showing a high level of "I don't have a clue'! I landed ahead of him & then he came in about 2 mins afterwards, downwind LDG I might add. I tried to call him on the radio whilst he was taxiing in (low workload for him) just to help him in some way (cause this guy was dangerous to others)but he never said boo & parked well away from the normal GA area. Now that's a worry! I know it's a little off topic but in some ways all the fancy instruments won't help you when there are pilots out there with such little knowledge. Oh btw before some of you get on yr high horses the A/C in question was a C210, an A/c that ought to have been flown by someone whom was switched on, 160kts is not to be sneezed at!
TCAS was for many years not considered for the SE Section's A/c due cost & the fact that being presented with multiple targets in & around a busy CTAF actually can work against you in a SP environment. The eyes & good training/airmanship by ALL is yr best defense
Wmk2