It really depends on what the benefits of bypassing the detection are and if those benefits can be had elsewhere at lower cost. For ticket sales or limited run product sales or similar things, the benefits of buying (and presumbably reselling) the limited item is high, and there's a limit to what you can do to detect humans (and as you've described it can be counter productive). For spam prevention, making it cost more to spam means spammers are encouraged to find somewhere else to spam, which is good for your users (while using your product anyway). But it won't stop everything, some people are going to manually type their spams, and some people will build robots to tap out their spams more like a person; and if you ruin the experience for users (especially new users) that doesn't work either; a network with zero messages is spam free, but doesn't help anyone.