I worked for a flying school that was not bad, but far from the most careful or strict I ever came across, especially under my first CFI. However they would never have allowed, let alone encouraged, anyone to take off in a Cherokee 140 with 4 adults on board! Full fuel just compounds the stupidity. Encouraging a basic PPL holder to fly into IMC, when it was clear that VFR flight was impossible, well it beggars belief. Even that CFI, who flew some marginal VFR himself, would not have flown VFR much less allowed a hirer to fly in the conditions (hirers were monitored until the club was happy, usually 100 hours or so. Other clubs they are always counter-signed).
Check weight, check fuel, check weather. Every flight.