I read (well skimmed) their manifesto before e-mailing my MP and it is pensions and winter fuel allowances and NI tourism.

I don't think they could actually force the House of Commons to undo all the women's rights, environmental and LGBT progress of the past decades but an alliance shifts the boundaries of what sort of opinions are acceptable in the same way that the Brexit vote made it possible for people to reveal their racism in public. There was an English Tory voter on Any Answers yesterday saying an alliance with the DUP would be good because Christians* are persecuted by being unable to hold their homophobic religious views in the workplace. It shifts the climate rightwards and we've seen how quickly that can happen without us noticing.

And that's quite apart from it making it impossible for the UK government to mediate in NI.

Anyway at the point of typing they don't seem to be managing to agree...

*I know far from all Christians