It's considered less secure because now there is another way for someone to intrude into your Google Account if the application isn't secure(that and it isn't YOU specifically accessing it).
Sadly because you put that script there, then there really isn't a way to make this secure without somehow forwarding the CAPTCHA and answering it every time. The reason for this is now they have no way to prove that the application accessing your account is not a bot, but an actual person. They also have no way of making sure that your application hasn't been hacked, replaced, injected into, intercepted, ETC, ETC. So yes, it is less secure without a CAPTCHA, and you can't make it more secure because it's not you.
Now what you're doing isn't BAD, but be for warned this can open you up to possible attacks with people using this SMTP relay to try and brute force your account. As long as you know what you are doing, and the possible dangers of it, it's fine. Just take steps to keep yourself, your business, your other stuff... safe and secure.