Like any other effect, compressors are a tool. Whether you need/want that tool depends on your application and your goals. Like with any tool, you should consider what job it is that you want done, and decide if a compressor is the right tool for the job. Just because there are other players here who say they never use one (or always use one) doesn't mean that's what you should do; you might not have the same job in mind that they do.
For instance, some (maybe many) compressors color the sound in some way, and if you want that coloration, then of course you'll want one.
Even without obvious coloration, some songs are recorded with an enormous amount of compression and if you're interested in getting that sound, you'll need a compressor.
And this thing about compressors only being to make up for bad technique... bunk. Listen to Tony Levin's bassline on "Sledgehammer"—it's compressed super-hard. (Apparently it was compressed on the way in, and then compressed again in post.) Is Tony Levin's technique bad, such that it needs to be covered up? Uhh, I'm going to go with "no" on that one. The compression is there because the goal was a super-compressed sound. (Personally I love this bassline—terrific fun to play, especially the last third of the song after the second chorus—and I put on a compressor for it, drop the threshold low and go 10:1. It just sounds wrong if not crazily compressed. It'd be like playing "For the Love of Money" without a phaser. I mean, sure, you can, but it won't be quite right, will it?)
There are other applications as well. As has been said, lots of engineers (FoH or recording) will compress the bass regardless, and you may want to take control of that rather than leaving it entirely to the engineer. Lots of other examples throughout the thread—but maybe none of those apply to you. If not, then nope, you don't need a compressor.