Your use of the words poor or fallacious are indeed poor. There is a huge difference between

a) the usual situation where some people don't participate in a regular referendum or election that most of the population and all authorities support as constitutional, and then

b) the situation in Catalonia where the referendum is only considered legal by some of the authorities, where other authorities have told voters to refrain from voting and are actively trying to prevent the voters from voting, and where a presumed 40-50 percent of the "electorate" don't even believe it's constitutional.

Let's not pretend that people that would vote "remain" are likely to participate in a vote they have been told by the some of the authorities not to participate in. Only the "leave" voters who believe the referendum is legal in the first place have a clear incentive to participate in it.