Pilot reported that a large number of paragliders frequently flying in an area pose potential airborne conflicts with transiting aircraft.

Narrative

The paragliding club puts up literally dozens of paragliders simultaneously that completely block air navigation through ZZZ south of ZZZ1. This is especially hazardous when the ceiling is below the ridge line as it was on Date. The NOTAM for glider activity doesn't let pilots transiting the area understand the nature of the hazard presented by dozens of paraglider operating at once from the cloud base to the ground in a narrow gap in the hills. Anyone that's not familiar with the hazard is likely to have an accident or near-miss. It's like a drone show at Oshkosh.The club likes to claim operation under Part 91 when it's convenient and under Part 105 when that suits their purposes. I don't remember paraglider operators having to obtain a private pilot certificate with a glider rating; and paragliders and conventional gliders have dissimilar operating characteristics. Permitting club ops under Part 91 seems a stretch and definitely unsafe. The paragliding operation at ZZZ2 more closely resembles a mass jump operation conducted by a large aircraft operator over an airfield over other drop zone; except there's no radio calls to warn nearby fixed-wing aircraft. The density of paragliders in the gap over ZZZ makes it difficult to avoid them once you're stuck in the valley under the cloud deck.Some government agency needs to specify which set of rules paragliders have to play by. The laissez-faire FAA approach to regulating paragliders is the classic hole in Reason's swiss cheese safety model.