A Guy Called Tyketto wrote:

If ATC tells you to remain outside you have to remain outside, whay
requires you to read it back?


Because if you don't read it back, they have no way to know
that you have acknowledged their call to you.

Believe me, if ATC gives me an instruction and unless I respond to
the contrary they assume that I've heard and will comply. The sole
exception to this is runway hold-short/crossing restrictions.


Where's the requirement for radar contact? Where's the requirement for a
readback?


For class C, they will always tell you 'radar contact
location, say altitude'

No they won't. Not in any stretch. They'll only tell you radar
contact if you are indeed in radar contact. This usually happens
after a transponder code is issued etc.... None of this has anything
to do with your operating in class C airspace.

Class B, they'll tell you 'radar contact
location, cleared through/into xxx Class B airspace' along with an
altimeter setting for the major airport in their area.

Again, RADAR CONTACT is a different concept from either the clearance
or the altimeter setting. The altimeter setting will be that of what
they are using (which may or may not be associated with an airport).

That is a
requirement for ATC to give you when entering Class B or C airspace.
See the 7110.65, sections 5-3-1 through 5-3-6. There's the requirement.
If they tell you to remain outside a given airspace, you had best
readback that you are remaining outside that airspace. 7-9-2 gives
leeway for the readback.

No, those sections don't have anything to do with entering airspace.
This is again a fundamental issue you seem to fail to want to
understand. Radar service is a service. The airspace indicates
where you might expect to find it, but the authorization to operate
in any given airspace is NOT dependent on RADAR SERVICES being offered.
I've operated out of the primary airport of a CLASS B airspace with
NO RADAR SERVICE POSSIBLE (my transponder was out and their primary
radar was out at the same time).