Tactical voting can actually get you an outcome the nearest to what you want.
In the 2015 election, South Thanet was a genuine three way split between Ukip, Conservative and Labour. (That's the constituency where Farage stood and which is now being investigated for electoralfraud by the Conservatives, in case people had forgotten.)
Labour was the lowest of the three. My preferred options would have been LibDem or Green, but they didn't stand a chance. If I had lived in South Thanet, I would have wanted Ukip like a hole in the head. Farage's face and voice make me want to vomit.
Therefore, I would probably have voted Conservative (gritting my teeth), as many people did. My reasoning would have been that Conservative was closer to what I wanted than Ukip. That's how a mature democracy works. People have to make compromises all the time, despite having the right to choose. Tactical voting attempts to produce the outcome closest to what an individual wants. It's not an episode of "Bake Off" or an FA Cup Final.
The FPTP sysyem means that the majority of the popular vote is nearly always opposed to the party which wins. I have no doubt that the Conservatives will win the most seats in this election, but it's not democracy when they only represent about 25% of the electorate (as they do now). Tactical voting attempts to unite the opposition and create more democracy.
Coalition government works well in Germany, but even the government has to make compromises. Tactical voting puts the responsibility for the compromises in the hands of the electorate. The French system means that the second round inevitably involves compromises and, hopefully, will keep Le Pen out, even if she does win the first round.
PS.There's been a dramatic increase in the number of 18-35 year olds who have registered to vote over the last few days.