I'm on the side of safe skies for everyone, but I sense from the replies there is not a universal strongly supported case for change. Surprising. It is still an open debate. OK, but let us have that debate and analyse the merits of both sides. Let us NOT just bumble along hoping it'll be alright.
In the US that debate was resolved by the early 90s based on real world experience, and occurred between over a roughly 15 year period initiated by two airliner/GA mid-airs over major cities in Southern California (in 1978 and 1986). Mode C transponders are generally required above 10,000 ft, and near large airports up to 10,000 ft. Airliners must have TCAS and use it as they pass through mixed IFR and VFR non-communicating aircraft in the Class E that covers most of the US below 18,000 feet. The system has proven to work in airspace with very high GA utilization and did not require Mode S or separating airliners into their own radio communication mandatory airspace.
Negative transponder aircraft with no engine driven electrical system are exempt from the Mode C transponder requirement above 10,000 ft in the US. Some feel that particular exemption, for sailplanes only and not powered aircraft, should be debated. There is no push from anybody influential for airspace changes that would preclude airliners from mixing with VFR non-communicating (or non-radio) traffic in Class E.
I think the biggest issue in the EU is non-uniorm airspace between countries, making it near impossible for any international IFR pilot to remember the rules and expectations for traffic avoidance when operating at any given airport. A simple, uniform Pan-EU airspace structure would add more safety than any overdone system that separates airliners from everybody else, or demands radio communication.