Sinema's vote killed Democrats' last, best hope to protect American democracy. She cites concern about future Republican actions unhindered by the filibuster, but they're already enacting voting restrictions at a state level that could be stopped by a reform bill.
Sinema is entitled to favor the filibuster over a system with unchecked majority control. She has the freedom to vote as she wants. Censuring her is the culmination of a pathetic tantrum by a party that can't get its way.
Censuring Sinema is another example of the ideological purity push that's making Washington dysfunctional. Actions like this show Democrats and Republicans are catering to the extremes of their parties. They neglect moderate and independent voters at their own peril.