I don't think they 'should'. There doesn't need to be a rule. I am amused by the 'aubergine hue' thing above, however! I think lots of men who do dye their hair to disguise the white or grey tend to go a shade too dark so that clashes with their changed skin pigment and results in a very ageing and draining look. Perhaps they are less cosmetically aware than women and that's why they can be a bit clumsy? Mind you, those women with the square or slug-shaped eyebrows seem similarly unaware... My dentalist is trying to get a wrinkle I have betwixt my eyebrows filled and it seems a reasonable suggestion (though I doubt I will have it done). I don't see anything wrong with a man wanting to fight the Reaper and cheat a few years away similarly to how women seem to be able to more freely.
Supposing someone has deep wrinkles and they look 20 years older than they are? This can affect relationships.
I know of people under 35 who look much younger as a result of botox.
Why only women? Some men go grey in their 20s and get wrinkles so why can't they compete on a level playing field with all the botox'd, hair dyed women smothered in makeup?
I can think of quite a few people who would benefit from botox, male and female.