Cutting your nose off to spite your face

I don't understand.  The Guardian reports:

The prospects of Labour opposing British membership of the European Union, or adopting a position of neutrality, has grown markedly after the Trades Union Congress (TUC) voted to recommend Britain leave the EU if David Cameron negotiated a new European settlement that watered down workers’ rights.

To lose the protection of the EU Social Chapter would indeed have a deleterious effect on workers' rights; but I do not see that leaving the EU would do anything to restore the position to status quo ante.  If anything, it would give a Conservative government greater freedom to worsen the position of workers.