Is that fear irrational? Let me state some facts:
1. Elon Musk is in full control of Starlink
2. Elon is politically aligned with Trump
3. Trump is pressuring Ukraine by taking away any US support. He paused military equipment delivery that was already approved, and now cut intelligence sharing.
It doesn't seem that far fetched that they would use cutting Starlink in these negotiations.
A counter argument could be that Elon still wants to get revenue for this (I think Poland is paying for it).
In my opinion, Starlink is a threat to European security, in an ever growing hostile US. Remember that Trump explicitly didn't exclude taking EU territory by force.
Even if Starlink isn't cut, they would most likely use it in their negotiations for Ukraine to "peacefully" surrender (partly) to Russia.