should i hard support in pubs

i have been practicing hard supports like CM,omniknight,vengeful,shadow shaman.

can i successfully support in a pub game or should i just stick to semi support heroes like ES ?

Yes, you will make a lot of friends if you support well. As a general rule, you should learn all roles, especially if you're newer to dota, you'll be amazed at how easy games are in the beginner tier when you have map vision. Vision wins games, but then again if your team can't quite figure out positioning and coordinate than it's still bad news bears but you'll be able to support and guide them to fights and such with less attention spent on farming

Yes, because many teams will pick too many carries and be extremely farm dependent. Trying to play a semi-support who needs to do a hard support job in those circumstances is very difficult, as you won't be able to get the items you need.

Yes, you should, because:-

1. You have a better understanding of your Teammates and enemies in general, e.g. If you don't know how Supporting works, how can you know when it's a good idea to Initiate with only 2 Supports for backup?

2. By learning every Role, you'll inevitably learn how all the Heroes in the game work, and how to fight them, e.g. when do you expect the other Team's Supports can start Roaming and Ganking effectively, and what do you need to do in order to avoid Feeding them?

3. It's a LOT more fun than Carrying. Compared to sitting in a Lane, Last Hitting, you have to think about Zoning Out the Offlaner, Roaming to Mid and Offlane for Ganks, extreme Mana Management, how to make the most of your little Gold, finding ways of getting Exp without disrupting your Team, etc. etc.

depends...what kind of level are we talking about?

i mean ...yes, vision wins games.... but if we are honest even an ES can put up 2 wards every 4-6 minutes....
if we are talking about games were there are instantly 4 carry picks in each team i would not advise going for a hardsupport (meaning warding, counterwarding, buying teamfight items, smoke, dust ..etc, etc.), as its just to frustrating seeing all your effort gone to waste, because of carries that cant appreciate / utilze a well played support.

Yes you should, but dont hesitate to be greedy, if you can get farm becouse your carry is not carrying a TP while a huge wave is approaching, just farm it, dont let it go to waste becouse you are the 5 position.

Play a Crystal Maiden seriously, her lane presence is amazing , and if you continually net kills and assists be greedy, in lower tier pubs, everyone is greedy. Get your items like Shadow Blade and Black King Bar invis, pop bkb and ulti. Watch everyone die, and call yourself princess of ice murder. Other supports that can afford to be greedy in these games and can actually just wreck face are Rubick Ogre Magi Warlock Lion Lina Shadow Shaman Leshrac Shadow Demon. They have abilities that will piss off the other team and probably net you a decent amount of kills. Warlock absolutely wrecks **** in the new guy tier. Lion and Lina have big ultis to net those early kills, etc. So yes I agree, be greedy, just don't forget to ward every once and awhile.
When I started playing HoN back in the day I had played dota on wc3 like maybe 10 times..throwing 1 decent ward up and watching a mid just stand there and waste time, while you rotate on him and blow him up is pretty funny.

I hard support in a lot of games and sometimes it's what wins us. I once saved a Venomancer from certain death from an Ursa + Silencer surprise gank just by knowing when to use Leech Seed, Living Armor and Overgrowth at the right time. We both escaped after that. Had I picked Anti-Mage instead of Treant Protector, I probably would have just blinked away and gotten Venomancer killed and it would have cost us a game.