Yes it is. Without isolation every part of that circuit should be considered to be connected directly to the main, with the potential of upwards of 20A of current at 240V potential. It can be lethal.
The OP came across an nonchanlant about the safety issue. That's the reason for being vociferous.
But I don't believe the OP was one of those folks. Anyone trained on high voltage/high current equipment have a healthy respect for the safety issues involved. The OP's apparent disregard for such safety issues is what raised the alarm bells in my mind.
No. Each are potentially lethal and have specific safety procedures for building, using, and servicing such equipment. Right?
Can we at least agree that the attitude inside such equipment should not be "no big deal"?
Several issues here:
1) The OP wanted to drive a relay. It isn't clear that the cap can provide enough current to drive it.2) The enclosure is the only isolation. Everything inside that case needs to be considered to be at line potential.
3) The OP said he wasn't concerned about safety issues.
The only point I got from the discussion was that he was concerned about the size of he circuit.
BAJ