If huge profit-making companies like Disney, Coca-Cola and McDonald's spend so much on marketing and sales, then it must be profitable. Similarly, there's no reason that fundraising spend wouldn't be financially advantageous to a non-profit.
If you support Wikipedia enough to donate, then it makes sense to want them to raise as much as they can. In which case you should enthusiastically support them running like a business-savvy organization.
The spend on fundraising does go towards the mission, because it increases the amount of money for the mission. You're making the incorrect assumption that donations are constant.
Imagine that a charity hiring a fundraiser for $50k garnered $150k of additional donations. Let's say without that fundraiser, they got $100k in donations. So with the fundraiser, they got $100k + $150k - $50k = $200k net to spend on the charitable purpose.
20% of all donations go to the fundraiser's salary while she's employed. But if the fundraiser is sacked, then 100% of donations go to the mission, yet the mission takes a loss of 50%.