If you can afford to take the risk, meaning if you won't be kicked out of your place in three months, you have absolutely nothing to lose by taking the chance. You can always get a part time job later. Or a full time job a year down the line.
I'm sorry, are we both existing in the same economy? Because I'm seeing 90 graduates apply for every graduate post, and some 600-800 people applying for each non-skilled post. So, don't kid yourself, the days of qualified and experienced people getting a job at the drop of a hat are long over.
I wouldn't bank on getting another job easily. This is why planning ahead and not acting recklessly is the best option. If you go full time, make sure you have the resources to see you through just incase it doesn't work and you suddenly find yourself unemployed in the middle of a recession and trying to explain to potenial employers that you quite your last job because you wanted to be a full time writer.
And gaps in employment are the norm now, and never were fatal. It never did take much imagination to fill in gaps, especially when you can legitimately put down "self-employed".
Yes and no. Gaps now are the norm - which is why you should try not have them. Keep working, keep yourself relevant to the current workplace.
I really despise the implication that those of us who write full time are impractical, selfish, or irresponsible.
No one said that, however, I would like to address your point. Those who write full time and can afford to - great. Those who can't really afford to, well that's a different story.
You do need to consider how any employement choice effects others - from income, to stability to benefits and healthcare etc.