allowing taps on systems and having to reconfigure your system to facilitate this are completely different issues.
a wire-tap with cause is ok (and in the case of certain payphones, they are generally ones that have been used for drug trafficing. so while they may not have probable cause to listen to each person, the argument could be made that they have probable cause for the phone).
but forcing you to set up a system for easy snooping is just too damn much. it's like requiring you to build peep-holes into your house, so that if they feel the need to check up on you they can do it easily.
If someone is going to invade my privacy, or violate my rights, I'd prefer it was as difficult and costly for them as possible.