The early stuff was spy satellites, weather satellites, and communication satellites.
The earliest active communication satellites — e.g. Telstar 1 — was done with "take signal in from vaguely the right direction, amplify with pure circuitry, rebroadcast in vaguely the right direction", no encryption possible on the satellite itself, and the thing itself was so primitive it was spin-stabilised rather than having an actively maintained orientation.
Weather satellites won't have mattered too much. Spy satellites I'm not sure about (what with this stuff being somewhat secretive and all), but they're obviously a thing where security matters.
These were and are called "bent pipe" satalites as they deftly turn around an amplified signal. But their control circuits are different and are not so open.
For the airplane nerds, this was also how early radar jammers worked. They took an incomming radar signal, delayed it a little, and retransmitted. No processing required and no digital circuits. That worked very well once upon a time.
Sure but that was so propaganda heavy nothing can be trusted from that era. What do people actually think today and why? Surely we live in such a free society now people are actually free to explain their viewpoints and reasoning.
Besides, invoking the cold war explains little (aside from invoking the propaganda of the time). The soviets live-streamed the moon landing. The idea that they were necessarily antagonistic is simply inaccurate. Not to mention what they would gain from fucking with satellites remains unexplained.
You might have chosen a bad example, as both sides had many early warning satellites, and such a catastrophic 'failure' in any tactically significant proportion of them would immediately put both sides on high alert. It would be much more valuable to target individual reconnaissance or communications satellites in order to make a 'blind spot' to support a particularly important secret project, but even this scenario would be scarcely credible.
Does space race say anything to you? One way of winning a race is to become faster, another is to make others slower. You know sabotage isn't just spy novel stuff.
Compared to what? What was (or is) worth securing? From what? Talking about security in abstract is nonsensical