Note, I've only used GM8 and above. Mostly I use GMS.
I mean I'll say that if you want 3D I'd seriously consider Unity or UE4 over Gamemaker. Multiplayer is also a little limited with GM. (Both are possible of course though).
But other than that, Gamemaker is at least a completely valid option, and I'd daresay superior than most other options.
I've had friends say, "I'm going to make a game too! And I'm better than you, because I use a real engine". Some have said they're making their own engine. And my response is, "If that's so much better, how come I have games finished and you don't?" Some of my friends seem to think they must be better programmers than me because they know formal Java and can make a text adventure game in eclipse. I've watched them program stuff, and I don't think they actually know how to use "if" statements sometimes. The reason I don't bother with Eclipse much is that GMS is soooo much faster to do the same stuff.
Another point to make is that AAA companies don't use Gamemaker. They use Unity or UE4 or other things. So if you want to be hired by Nintendo, GM experience doesn't count for as much as we'd all like. Also, GM does have a lot of high quality games, but still not as much as other options. That has more to do with the number of users than anything. But also percentage wise, the fact that GM attracts so many non-serious programmers, the overall percentage of good games coming from GM is lower, because they're diluted by all the lame ones.
I think people think we're taking the easy path. Which is true of course, and the easy path is usually held in low regard. But just because we can make a game in 15 seconds doesn't mean we stop there, that'd be stupid. No, while everyone else is making those same 15 second games over several months, the rest of us make a full scale RPG and publish it on Steam. I think it's an issue of the "pros" distancing themselves from the "noobs" whereas the true pros ignore that separation and just make games.