With respect, like HC I think your reading of this piece is miles off.
The whole focus of the piece is on the Labour party position and specifically, in the in the paragraph you've quoted, the electoral effect of the LPs position.
(My emphasis) Timoney is arguing (counter Wren-Lewis) that the LP not taking a more Remain stance (or more specifically calling for a second referendum) is not going to result in the loss of many voters.
As he summarises in the second to last paragraph
I do not think it's fair to say that Timoney thinks you should be "dismissed", but on a crude electoral level yes Labour probably can "dismiss" the small minority of voters that are such strong "remainers" that they will vote for the LDs or Greens in protest of the LPs stance on the EU (at least in England and Wales, the situation in Scotland is obviously a bit different). From the perspective of electoral calculations your vote (and mine) certainly matters much less than the votes of people in, say,
Pudsey or
Shipley. We are in safe Labour seats, the same seats (generally) that the die-hard remain vote is concentrated, a minor loss of support in our seats is neither here nor there, whereas if Labour want to win a GE they certainly need to be winning Pudsey and ideally want to take Shipley too.
For all the claims by polticians, the media and LDs that the UK leaving the EU is the greatest issue of our times, it certainly wasn't to most voters at the last GE. For all the daft talk of LDs removing Hoey, she ended up with a swing towards her. Many Labour voters may prefer a more Remain stance from the party but is that going to mean that come election time they don't vote/vote for someone else? IMO only in a small minority of cases, and mostly where the LP can afford it.