Are Party members who don't vote Labour 'scabs'?

Since joining the Labour Party I have learnt a lot and my experiences from being actively involved has dramatically developed my thinking. The way 'activists' and 'The Party' should treat its own members is one of them.

The Rule Book is quite clear about members who lend their support to opposition forces:

'A member of the Party who joins and/ or supports a political organisation other than an
official Labour group or other unit of the Party, or supports any candidate who stands
against an official Labour candidate, or publicly declares their intent to stand against
a Labour candidate, shall automatically be ineligible to be or remain a Party member'

Which in theory makes indisputable sense because if you are a member of an organisation it is self defeating to vote in opposition to it and could be an indication you aren't truly supportive of it.
However UK voters and even Labour Party members don't live in the realms of theory but in the real world where things are often more complicated. I will set out a few examples of this below and although I don't necessarily agree with all of them they are at least valid points of view that many people have.

Tactical voting
The First Past the Post voting system has created a situation of safe seats and marginals where in reality overall election results are swung by a small numbers of votes. In many elections it is very hard to change your representative and often there is only one alternative way to vote that might do this. For this reason many people vote tactically like the estimated 6.5 million in the 2017 General Election. So if you are a Party member why is it any different? People don't want to waste their vote and would rather the 'lesser of two evils' if they can't see their favourite party winning.

Some candidates aren't very good
Ever political party has this same issue and it normally directly correlates with the size of the party in different areas. For example in an area where Labour dominate the Conservatives will likely have few members locally so it is harder to find good candidates and this is exacerbated when often a party will want to stand a candidate at every election.

Labour is a 'broad church'
Labour has always been a coalition of different ideologies and traditions so it includes a wide variety of people. This can mean a member can find their local candidate has some very differing views to them and even that another candidates views are more aligned with theirs.

Single issues
Some issues are so big that they become vitally important to an individual eg the EU, war, the environment and large planning applications etc. Sometimes party members might have the opposite view on such large issues while being in agreement with a different candidate. 

There are lots of counter arguments to the above reasons, which are applicable to all the larger UK parties, sometimes these debates need to be had however often such debates can come across in a very negative manner which is not very inspiring or persuasive. What I am more concerned about however is when a small minority of often vocal activists call members who are even fleetingly considering not voting Labour scabs, traitors and other insults or generally portray a hostile attitude, reach for the rule book and say they should be thrown out the party. Telling someone, even a party member, they HAVE to vote Labour is not persuasive but damaging. I have seen first hand how this puts off members and other voters who hear about it.

I am not necessarily suggesting Labour rules need to be changed only that if members aren't sure about voting Labour they are approached with respect, understanding and a positive argument as to why they should vote Labour. This attitude might change their mind where as a hostile one will only alienate them. This is something that doesn't only occasionally happen in the Labour Party but other political parties too.
Labour generally is a fantastic positive force for good and this is why people should vote for Labour.