“remain loyal to their party” Is that good? Why should each person have a party? You should stay loyal to the policies you care about, and see which party shares the most of them (and 2nd preference if there is a party that also meets most of them)
“switch or vote tactically to get the result that the nation collectively wants or needs” Voting tactically in switching your vote requires guess work on how the votes are going to go(and this is often done with the aid of graphs designed with lies in them). AV allows you to effectively switch your vote once the information is available (once 1st preferences have been counted).