Not having a go at you, but this is a really odd stance that many people have taken - in the sense that, if you were talking about the Tories, no-one would say that they like May, or that there was anything in the manifesto that they rated either.
Correct they wouldn't, she's bloody awful. Without trying to defend them, there isn't much in the conservative manifesto that means there will be massive change that could really upset the apple cart from how it is now.
Labour could get in and enact their policies and all could be fine, but it will be one of the hardest parliaments outside of wartime. It is a risk to try and squeeze tax and hope the economy will grow (or stay the same) with the unknows that brexit will bring.
The way I look at it is if Labour wins they run the risk of being unelectable for a long period should things go wrong. So what is better from a Labour point of view? Let the Tories have at best 5 more years and by then everything will be settled in terms of knowing what damage (or not) has been done by leaving the EU giving Labour a better chance of creating a better financial plan to decide what can be done OR get in now and then be forced to firefight a mess they didn't actually create.
It is a quandary, but it's a bit like the lib dems going into government as a coalition, was it worth it in the long run? However i do understand the argument that if they don't get in now while they have a chance, there is a risk if suddenly the country booms after brexit.