There have been some very good posts on how to assess if a friendship is appropriately boundaried, etc, etc. I've certainly had the "so-called platonic friend isn't interested in friendship after I mentioned I'll never be a prospect" experience.
Some men/women are fairly desperate for attention, any attention, so its unwise to develop a 1-1 connection with them, as they'll bite your hand off ('they kissed my cheek for a bit too long, that must mean they love me')
Some men/women tend to read subtext that isn't there or are fairly resentful/deluded people so will make up a whole romantic fantasy regarding their exs/that secretary/teacher who smiled at them
Acquiring good judgement on these things is a handy (and essential) life skill.
But whilst 'some' people have ulterior motives, I've learned a lot of people are genuinely capable of socially working within an asexual space?
They're either attached, or they know if they weren't, there'd be lots of options/people they could potentially date, so why latch onto an existing friend? Dates are ten-a-penny with the advent of Online Dating: friends for doing stuff with are probably more valuable.
I don't think all men spend most of their life in some horny/amorous fog finding women useless as people, unless they're a possible next conquest. I don't think all women find at the first sign of attention their silly little heads wobble and they can't resist.
I think - like any other social interaction - a male friendship should be managed (like someone said, don't go into any grey areas, make sure you're not slagging off your partner to them or drinking to excess etc etc). But just the same as any friendship/interaction could potentially damage your partnership: you need to risk assess, and take an active role in making sure nothing untoward arises?
For example, I do think that if the friendship isn't 'equal', as in one party is at the beck and call of the other, or clearly being used for favours/attention it should stop. Or if one party is fairly socially desperate, and basically sort of eyeing the others relationship in a baleful, resentful 'look what you've got' way, then RUN.