There was a criminal investigation into the sinking of that trawler, which was more cock up than deliberate.
EU also launched an investigation into its part in the sinking... for what that is worth.
What would you drop them off into? over the side onto that raft? all at gun point.
What happens when the French just tow them back? as they almost certainly would?
You would cause an international incident of huge proportions, 2 NATO members at near war with each other.... the EU would of course take sides.
No, far better to just tow the boats out to sea quietly, at night, sink them and drown the migrants, word would soon get back to Calais, we'd deny it of course, job done... is that what you want the UK to become?