This is actually a very good point that you bring up. According to G14:
G14. During the ENDGAME, don’t touch ROBOTS in their RENDEZVOUS POINT. During the
ENDGAME, a ROBOT may not contact, either directly or transitively through a POWER CELL, an
opponent ROBOT whose BUMPERS are completely contained in its RENDEZVOUS POINT and not
in contact with its GENERATOR SWITCH.
Violation: TECH FOUL
So it would be viable to take a Tech foul for preventing a Climb. However, this will likely generate C1 violations:
C1. Egregious or exceptional violations. Egregious behavior beyond what is listed in the rules or
repeated violations of any rule or procedure during the event is prohibited.
In addition to rule violations explicitly listed in this manual and witnessed by a REFEREE, the Head
REFEREE may assign a YELLOW or RED CARD for egregious ROBOT actions or team member
behavior at any time during the event. This includes violations of the event rules found on the FIRST®
Robotics Competition Event Experience web page
Please see YELLOW and RED CARDS for additional detail.
Violation: The Head REFEREE may assign a YELLOW or a RED CARD.
So you might be able to get away with this for one match at early events, but head refs should be aware of this strategy and see it as a C1 violation.
A bigger issue that I see is that there is no penalty for contacting an opposing robot that is partially in their Rendezvous Point.
an opponent ROBOT whose BUMPERS are completely contained in its RENDEZVOUS POINT
This means that as the rules stand right now, a team can park in their opponent’s Rendezvous Point and prevent them from entering. As long as the defending team doesn’t allow their opponents to completely enter their Rendezvous Point (bumpers and all), they can prevent hangs. You would have to be careful of this situation, but it is a perfectly legal strategy that I hope gets corrected in a Team Update.