two important things to keep in mind here
1) everyone loses if cycling/baseball-level of doping is discovered, atp, players and fans. lets say 6 out of top 10 are found guilty, sport will never recover. you can always find another homerun slugger to root for, and most of cyclist are anonymous anyway, but tennis is much more personable
But the longer tennis persists with its head-in-the-sand approach, doing near no testing at all, the more the above scenario becomes an inevitability. We will get to a stage where the entire top 25 is doping, because nobody else can compete with the power and endurance.
Then when it eventually does come out, the collapse will be all the bigger. We also run the risk of the arms race that happened in cycling: lots of deaths, and a permanent tainting of the sport.